Provided by: libdbd-sqlite3-perl_1.74-1build3_amd64 bug

NAME

       DBD::SQLite - Self-contained RDBMS in a DBI Driver

SYNOPSIS

         use DBI;
         my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");

DESCRIPTION

       SQLite is a public domain file-based relational database engine that you can find at
       <https://www.sqlite.org/>.

       DBD::SQLite is a Perl DBI driver for SQLite, that includes the entire thing in the
       distribution.  So in order to get a fast transaction capable RDBMS working for your perl
       project you simply have to install this module, and nothing else.

       SQLite supports the following features:

       Implements a large subset of SQL92
           See <https://www.sqlite.org/lang.html> for details.

       A complete DB in a single disk file
           Everything for your database is stored in a single disk file, making it easier to move
           things around than with DBD::CSV.

       Atomic commit and rollback
           Yes, DBD::SQLite is small and light, but it supports full transactions!

       Extensible
           User-defined aggregate or regular functions can be registered with the SQL parser.

       There's lots more to it, so please refer to the docs on the SQLite web page, listed above,
       for SQL details. Also refer to DBI for details on how to use DBI itself. The API works
       like every DBI module does.  However, currently many statement attributes are not
       implemented or are limited by the typeless nature of the SQLite database.

SQLITE VERSION

       DBD::SQLite is usually compiled with a bundled SQLite library (SQLite version 3.42.0 as of
       this release) for consistency.  However, a different version of SQLite may sometimes be
       used for some reasons like security, or some new experimental features.

       You can look at $DBD::SQLite::sqlite_version ("3.x.y" format) or
       $DBD::SQLite::sqlite_version_number ("3xxxyyy" format) to find which version of SQLite is
       actually used. You can also check DBD::SQLite::Constants::SQLITE_VERSION_NUMBER().

       You can also find how the library is compiled by calling DBD::SQLite::compile_options()
       (see below).

NOTABLE DIFFERENCES FROM OTHER DRIVERS

   Database Name Is A File Name
       SQLite creates a file per a database. You should pass the "path" of the database file
       (with or without a parent directory) in the DBI connection string (as a database "name"):

         my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");

       The file is opened in read/write mode, and will be created if it does not exist yet.

       Although the database is stored in a single file, the directory containing the database
       file must be writable by SQLite because the library will create several temporary files
       there.

       If the filename $dbfile is ":memory:", then a private, temporary in-memory database is
       created for the connection. This in-memory database will vanish when the database
       connection is closed.  It is handy for your library tests.

       Note that future versions of SQLite might make use of additional special filenames that
       begin with the ":" character. It is recommended that when a database filename actually
       does begin with a ":" character you should prefix the filename with a pathname such as
       "./" to avoid ambiguity.

       If the filename $dbfile is an empty string, then a private, temporary on-disk database
       will be created. This private database will be automatically deleted as soon as the
       database connection is closed.

       As of 1.41_01, you can pass URI filename (see <https://www.sqlite.org/uri.html>) as well
       for finer control:

         my $dbh = DBI->connect("dbi:SQLite:uri=file:$path_to_dbfile?mode=rwc");

       Note that this is not for remote SQLite database connection. You can only connect to a
       local database.

   Read-Only Database
       You can set sqlite_open_flags (only) when you connect to a database:

         use DBD::SQLite::Constants qw/:file_open/;
         my $dbh = DBI->connect("dbi:SQLite:$dbfile", undef, undef, {
           sqlite_open_flags => SQLITE_OPEN_READONLY,
         });

       See <https://www.sqlite.org/c3ref/open.html> for details.

       As of 1.49_05, you can also make a database read-only by setting "ReadOnly" attribute to
       true (only) when you connect to a database.  Actually you can set it after you connect,
       but in that case, it can't make the database read-only, and you'll see a warning (which
       you can hide by turning "PrintWarn" off).

   DBD::SQLite And File::Temp
       When you use File::Temp to create a temporary file/directory for SQLite databases, you
       need to remember:

       tempfile may be locked exclusively
           You may want to use tempfile() to create a temporary database filename for
           DBD::SQLite, but as noted in File::Temp's POD, this file may have an exclusive lock
           under some operating systems (notably Mac OSX), and result in a "database is locked"
           error.  To avoid this, set EXLOCK option to false when you call tempfile().

             ($fh, $filename) = tempfile($template, EXLOCK => 0);

       CLEANUP may not work unless a database is disconnected
           When you set CLEANUP option to true when you create a temporary directory with
           tempdir() or newdir(), you may have to disconnect databases explicitly before the
           temporary directory is gone (notably under MS Windows).

       (The above is quoted from the pod of File::Temp.)

       If you don't need to keep or share a temporary database, use ":memory:" database instead.
       It's much handier and cleaner for ordinary testing.

   DBD::SQLite and fork()
       Follow the advice in the SQLite FAQ (<https://sqlite.org/faq.html>).

           Under Unix, you should not carry an open SQLite database across a fork() system call
           into the child process. Problems will result if you do.

       You shouldn't (re)use a database handle you created (probably to set up a database schema
       etc) before you fork(). Otherwise, you might see a database corruption in the worst case.

       If you need to fork(), (re)open a database after you fork().  You might also want to tweak
       "sqlite_busy_timeout" and "sqlite_use_immediate_transaction" (see below), depending on
       your needs.

       If you need a higher level of concurrency than SQLite supports, consider using other
       client/server database engines.

   Accessing A Database With Other Tools
       To access the database from the command line, try using "dbish" which comes with the
       DBI::Shell module. Just type:

         dbish dbi:SQLite:foo.db

       On the command line to access the file foo.db.

       Alternatively you can install SQLite from the link above without conflicting with
       DBD::SQLite and use the supplied "sqlite3" command line tool.

   Blobs
       As of version 1.11, blobs should "just work" in SQLite as text columns.  However this will
       cause the data to be treated as a string, so SQL statements such as length(x) will return
       the length of the column as a NUL terminated string, rather than the size of the blob in
       bytes. In order to store natively as a BLOB use the following code:

         use DBI qw(:sql_types);
         my $dbh = DBI->connect("dbi:SQLite:dbfile","","");

         my $blob = `cat foo.jpg`;
         my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
         $sth->bind_param(1, $blob, SQL_BLOB);
         $sth->execute();

       And then retrieval just works:

         $sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
         $sth->execute();
         my $row = $sth->fetch;
         my $blobo = $row->[1];

         # now $blobo == $blob

   Functions And Bind Parameters
       As of this writing, a SQL that compares a return value of a function with a numeric bind
       value like this doesn't work as you might expect.

         my $sth = $dbh->prepare(q{
           SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
         });
         $sth->execute(5);

       This is because DBD::SQLite assumes that all the bind values are text (and should be
       quoted) by default. Thus the above statement becomes like this while executing:

         SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";

       There are four workarounds for this.

       Use bind_param() explicitly
           As shown above in the "BLOB" section, you can always use bind_param() to tell the type
           of a bind value.

             use DBI qw(:sql_types);  # Don't forget this

             my $sth = $dbh->prepare(q{
               SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
             });
             $sth->bind_param(1, 5, SQL_INTEGER);
             $sth->execute();

       Add zero to make it a number
           This is somewhat weird, but works anyway.

             my $sth = $dbh->prepare(q{
               SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
             });
             $sth->execute(5);

       Use SQL cast() function
           This is more explicit way to do the above.

             my $sth = $dbh->prepare(q{
               SELECT bar FROM foo GROUP BY bar HAVING count(*) > cast(? as integer);
             });
             $sth->execute(5);

       Set "sqlite_see_if_its_a_number" database handle attribute
           As of version 1.32_02, you can use "sqlite_see_if_its_a_number" to let DBD::SQLite to
           see if the bind values are numbers or not.

             $dbh->{sqlite_see_if_its_a_number} = 1;
             my $sth = $dbh->prepare(q{
               SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
             });
             $sth->execute(5);

           You can set it to true when you connect to a database.

             my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
               AutoCommit => 1,
               RaiseError => 1,
               sqlite_see_if_its_a_number => 1,
             });

           This is the most straightforward solution, but as noted above, existing data in your
           databases created by DBD::SQLite have not always been stored as numbers, so this
           *might* cause other obscure problems. Use this sparingly when you handle existing
           databases.  If you handle databases created by other tools like native "sqlite3"
           command line tool, this attribute would help you.

           As of 1.41_04, "sqlite_see_if_its_a_number" works only for bind values with no
           explicit type.

             my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
               AutoCommit => 1,
               RaiseError => 1,
               sqlite_see_if_its_a_number => 1,
             });
             my $sth = $dbh->prepare('INSERT INTO foo VALUES(?)');
             # '1.230' will be inserted as a text, instead of 1.23 as a number,
             # even though sqlite_see_if_its_a_number is set.
             $sth->bind_param(1, '1.230', SQL_VARCHAR);
             $sth->execute;

   Placeholders
       SQLite supports several placeholder expressions, including "?"  and ":AAAA". Consult the
       DBI and SQLite documentation for details.

       <https://www.sqlite.org/lang_expr.html#varparam>

       Note that a question mark actually means a next unused (numbered) placeholder. You're
       advised not to use it with other (numbered or named) placeholders to avoid confusion.

         my $sth = $dbh->prepare(
           'update TABLE set a=?1 where b=?2 and a IS NOT ?1'
         );
         $sth->execute(1, 2);

   Pragma
       SQLite has a set of "Pragma"s to modify its operation or to query for its internal data.
       These are specific to SQLite and are not likely to work with other DBD libraries, but you
       may find some of these are quite useful, including:

       journal_mode
           You can use this pragma to change the journal mode for SQLite databases, maybe for
           better performance, or for compatibility.

           Its default mode is "DELETE", which means SQLite uses a rollback journal to implement
           transactions, and the journal is deleted at the conclusion of each transaction. If you
           use "TRUNCATE" instead of "DELETE", the journal will be truncated, which is usually
           much faster.

           A "WAL" (write-ahead log) mode is introduced as of SQLite 3.7.0.  This mode is
           persistent, and it stays in effect even after closing and reopening the database. In
           other words, once the "WAL" mode is set in an application or in a test script, the
           database becomes inaccessible by older clients. This tends to be an issue when you use
           a system "sqlite3" executable under a conservative operating system.

           To fix this, You need to issue "PRAGMA journal_mode = DELETE" (or "TRUNCATE")
           beforehand, or install a newer version of "sqlite3".

       legacy_file_format
           If you happen to need to create a SQLite database that will also be accessed by a very
           old SQLite client (prior to 3.3.0 released in Jan. 2006), you need to set this pragma
           to ON before you create a database.

       reverse_unordered_selects
           You can set this pragma to ON to reverse the order of results of SELECT statements
           without an ORDER BY clause so that you can see if applications are making invalid
           assumptions about the result order.

           Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02) enhanced its query
           optimizer and the order of results of a SELECT statement without an ORDER BY clause
           may be different from the one of the previous versions.

       synchronous
           You can set set this pragma to OFF to make some of the operations in SQLite faster
           with a possible risk of database corruption in the worst case. See also "Performance"
           section below.

       See <https://www.sqlite.org/pragma.html> for more details.

   Foreign Keys
       SQLite has started supporting foreign key constraints since 3.6.19 (released on Oct 14,
       2009; bundled in DBD::SQLite 1.26_05).  To be exact, SQLite has long been able to parse a
       schema with foreign keys, but the constraints has not been enforced. Now you can issue a
       "foreign_keys" pragma to enable this feature and enforce the constraints, preferably as
       soon as you connect to a database and you're not in a transaction:

         $dbh->do("PRAGMA foreign_keys = ON");

       And you can explicitly disable the feature whenever you like by turning the pragma off:

         $dbh->do("PRAGMA foreign_keys = OFF");

       As of this writing, this feature is disabled by default by the SQLite team, and by us, to
       secure backward compatibility, as this feature may break your applications, and actually
       broke some for us. If you have used a schema with foreign key constraints but haven't
       cared them much and supposed they're always ignored for SQLite, be prepared, and please do
       extensive testing to ensure that your applications will continue to work when the foreign
       keys support is enabled by default.

       See <https://www.sqlite.org/foreignkeys.html> for details.

   Transactions
       DBI/DBD::SQLite's transactions may be a bit confusing. They behave differently according
       to the status of the "AutoCommit" flag:

       When the AutoCommit flag is on
           You're supposed to always use the auto-commit mode, except you explicitly begin a
           transaction, and when the transaction ended, you're supposed to go back to the auto-
           commit mode. To begin a transaction, call "begin_work" method, or issue a "BEGIN"
           statement. To end it, call "commit/rollback" methods, or issue the corresponding
           statements.

             $dbh->{AutoCommit} = 1;

             $dbh->begin_work; # or $dbh->do('BEGIN TRANSACTION');

             # $dbh->{AutoCommit} is turned off temporarily during a transaction;

             $dbh->commit; # or $dbh->do('COMMIT');

             # $dbh->{AutoCommit} is turned on again;

       When the AutoCommit flag is off
           You're supposed to always use the transactional mode, until you explicitly turn on the
           AutoCommit flag. You can explicitly issue a "BEGIN" statement (only when an actual
           transaction has not begun yet) but you're not allowed to call "begin_work" method (if
           you don't issue a "BEGIN", it will be issued internally).  You can commit or roll it
           back freely. Another transaction will automatically begin if you execute another
           statement.

             $dbh->{AutoCommit} = 0;

             # $dbh->do('BEGIN TRANSACTION') is not necessary, but possible

             ...

             $dbh->commit; # or $dbh->do('COMMIT');

             # $dbh->{AutoCommit} stays intact;

             $dbh->{AutoCommit} = 1;  # ends the transactional mode

       This "AutoCommit" mode is independent from the autocommit mode of the internal SQLite
       library, which always begins by a "BEGIN" statement, and ends by a "COMMIT" or a
       "ROLLBACK".

   Transaction and Database Locking
       The default transaction behavior of SQLite is "deferred", that means, locks are not
       acquired until the first read or write operation, and thus it is possible that another
       thread or process could create a separate transaction and write to the database after the
       "BEGIN" on the current thread has executed, and eventually cause a "deadlock". To avoid
       this, DBD::SQLite internally issues a "BEGIN IMMEDIATE" if you begin a transaction by
       calling "begin_work" or by turning off "AutoCommit" (since 1.38_01).

       If you really need to turn off this feature for some reasons, set
       "sqlite_use_immediate_transaction" database handle attribute to false, and the default
       "deferred" transaction will be used.

         my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
           sqlite_use_immediate_transaction => 0,
         });

       Or, issue a "BEGIN" statement explicitly each time you begin a transaction.

       See <http://sqlite.org/lockingv3.html> for locking details.

   "$sth->finish" and Transaction Rollback
       As the DBI doc says, you almost certainly do not need to call "finish" in DBI method if
       you fetch all rows (probably in a loop).  However, there are several exceptions to this
       rule, and rolling-back of an unfinished "SELECT" statement is one of such exceptional
       cases.

       SQLite prohibits "ROLLBACK" of unfinished "SELECT" statements in a transaction (See
       <http://sqlite.org/lang_transaction.html> for details). So you need to call "finish"
       before you issue a rollback.

         $sth = $dbh->prepare("SELECT * FROM t");
         $dbh->begin_work;
         eval {
             $sth->execute;
             $row = $sth->fetch;
             ...
             die "For some reason";
             ...
         };
         if($@) {
            $sth->finish;  # You need this for SQLite
            $dbh->rollback;
         } else {
            $dbh->commit;
         }

   Processing Multiple Statements At A Time
       DBI's statement handle is not supposed to process multiple statements at a time. So if you
       pass a string that contains multiple statements (a "dump") to a statement handle (via
       "prepare" or "do"), DBD::SQLite only processes the first statement, and discards the rest.

       If you need to process multiple statements at a time, set a
       "sqlite_allow_multiple_statements" attribute of a database handle to true when you connect
       to a database, and "do" method takes care of the rest (since 1.30_01, and without creating
       DBI's statement handles internally since 1.47_01). If you do need to use "prepare" or
       "prepare_cached" (which I don't recommend in this case, because typically there's no
       placeholder nor reusable part in a dump), you can look at
       "$sth->{sqlite_unprepared_statements}" to retrieve what's left, though it usually contains
       nothing but white spaces.

   TYPE statement attribute
       Because of historical reasons, DBD::SQLite's "TYPE" statement handle attribute returns an
       array ref of string values, contrary to the DBI specification. This value is also less
       useful for SQLite users because SQLite uses dynamic type system (that means, the datatype
       of a value is associated with the value itself, not with its container).

       As of version 1.61_02, if you set "sqlite_prefer_numeric_type" database handle attribute
       to true, "TYPE" statement handle attribute returns an array of integer, as an experiment.

   Performance
       SQLite is fast, very fast. Matt processed his 72MB log file with it, inserting the data
       (400,000+ rows) by using transactions and only committing every 1000 rows (otherwise the
       insertion is quite slow), and then performing queries on the data.

       Queries like count(*) and avg(bytes) took fractions of a second to return, but what
       surprised him most of all was:

         SELECT url, count(*) as count
         FROM access_log
         GROUP BY url
         ORDER BY count desc
         LIMIT 20

       To discover the top 20 hit URLs on the site (<http://axkit.org>), and it returned within 2
       seconds. He was seriously considering switching his log analysis code to use this little
       speed demon!

       Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.

       For best performance be sure to tune your hdparm settings if you are using linux. Also you
       might want to set:

         PRAGMA synchronous = OFF

       Which will prevent SQLite from doing fsync's when writing (which slows down non-
       transactional writes significantly) at the expense of some peace of mind. Also try playing
       with the cache_size pragma.

       The memory usage of SQLite can also be tuned using the cache_size pragma.

         $dbh->do("PRAGMA cache_size = 800000");

       The above will allocate 800M for DB cache; the default is 2M.  Your sweet spot probably
       lies somewhere in between.

DRIVER PRIVATE ATTRIBUTES

   Database Handle Attributes
       sqlite_version
           Returns the version of the SQLite library which DBD::SQLite is using, e.g., "3.26.0".
           Can only be read.

       sqlite_string_mode
           SQLite strings are simple arrays of bytes, but Perl strings can store any arbitrary
           Unicode code point. Thus, DBD::SQLite has to adopt some method of translating between
           those two models. This parameter defines that translation.

           Accepted values are the following constants:

           •   DBD_SQLITE_STRING_MODE_BYTES: All strings are assumed to represent bytes. A Perl
               string that contains any code point above 255 will trigger an exception. This is
               appropriate for Latin-1 strings, binary data, pre-encoded UTF-8 strings, etc.

           •   DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK: All Perl strings are encoded to UTF-8
               before being given to SQLite. Perl will try to decode SQLite strings as UTF-8 when
               giving them to Perl. Should any such string not be valid UTF-8, a warning is
               thrown, and the string is left undecoded.

               This is appropriate for strings that are decoded to characters via, e.g., "decode"
               in Encode.

               Also note that, due to some bizarreness in SQLite's type system (see
               <https://www.sqlite.org/datatype3.html>), if you want to retain blob-style
               behavior for some columns under DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK (say, to
               store images in the database), you have to state so explicitly using the
               3-argument form of "bind_param" in DBI when doing updates:

                 use DBI qw(:sql_types);
                 use DBD::SQLite::Constants ':dbd_sqlite_string_mode';
                 $dbh->{sqlite_string_mode} = DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK;
                 my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");

                 # Binary_data will be stored as is.
                 $sth->bind_param(1, $binary_data, SQL_BLOB);

               Defining the column type as "BLOB" in the DDL is not sufficient.

           •   DBD_SQLITE_STRING_MODE_UNICODE_STRICT: Like
               DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK but usually throws an exception rather
               than a warning if SQLite sends invalid UTF-8. (In Perl callbacks from SQLite we
               still warn instead.)

           •   DBD_SQLITE_STRING_MODE_UNICODE_NAIVE: Like DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK
               but uses a "naïve" UTF-8 decoding method that forgoes validation. This is
               marginally faster than a validated decode, but it can also corrupt Perl itself!

           •   DBD_SQLITE_STRING_MODE_PV (default, but DO NOT USE): Like
               DBD_SQLITE_STRING_MODE_BYTES, but when translating Perl strings to SQLite the Perl
               string's internal byte buffer is given to SQLite. This is bad, but it's been the
               default for many years, and changing that would break existing applications.

       "sqlite_unicode" or "unicode" (deprecated)
           If truthy, equivalent to setting "sqlite_string_mode" to
           DBD_SQLITE_STRING_MODE_UNICODE_NAIVE; if falsy, equivalent to
           DBD_SQLITE_STRING_MODE_PV.

           Prefer "sqlite_string_mode" in all new code.

       sqlite_allow_multiple_statements
           If you set this to true, "do" method will process multiple statements at one go. This
           may be handy, but with performance penalty. See above for details.

       sqlite_use_immediate_transaction
           If you set this to true, DBD::SQLite tries to issue a "begin immediate transaction"
           (instead of "begin transaction") when necessary. See above for details.

           As of version 1.38_01, this attribute is set to true by default.  If you really need
           to use "deferred" transactions for some reasons, set this to false explicitly.

       sqlite_see_if_its_a_number
           If you set this to true, DBD::SQLite tries to see if the bind values are number or
           not, and does not quote if they are numbers. See above for details.

       sqlite_extended_result_codes
           If set to true, DBD::SQLite uses extended result codes where appropriate (see
           <https://www.sqlite.org/rescode.html>).

       sqlite_defensive
           If set to true, language features that allow ordinary SQL to deliberately corrupt the
           database file are prohibited.

   Statement Handle Attributes
       sqlite_unprepared_statements
           Returns an unprepared part of the statement you pass to "prepare".  Typically this
           contains nothing but white spaces after a semicolon.  See above for details.

METHODS

       See also to the DBI documentation for the details of other common methods.

   table_info
         $sth = $dbh->table_info(undef, $schema, $table, $type, \%attr);

       Returns all tables and schemas (databases) as specified in "table_info" in DBI.  The
       schema and table arguments will do a "LIKE" search. You can specify an ESCAPE character by
       including an 'Escape' attribute in \%attr. The $type argument accepts a comma separated
       list of the following types 'TABLE', 'INDEX', 'VIEW', 'TRIGGER', 'LOCAL TEMPORARY' and
       'SYSTEM TABLE' (by default all are returned).  Note that a statement handle is returned,
       and not a direct list of tables.

       The following fields are returned:

       TABLE_CAT: Always NULL, as SQLite does not have the concept of catalogs.

       TABLE_SCHEM: The name of the schema (database) that the table or view is in. The default
       schema is 'main', temporary tables are in 'temp' and other databases will be in the name
       given when the database was attached.

       TABLE_NAME: The name of the table or view.

       TABLE_TYPE: The type of object returned. Will be one of 'TABLE', 'INDEX', 'VIEW',
       'TRIGGER', 'LOCAL TEMPORARY' or 'SYSTEM TABLE'.

   primary_key, primary_key_info
         @names = $dbh->primary_key(undef, $schema, $table);
         $sth   = $dbh->primary_key_info(undef, $schema, $table, \%attr);

       You can retrieve primary key names or more detailed information.  As noted above, SQLite
       does not have the concept of catalogs, so the first argument of the methods is usually
       "undef", and you'll usually set "undef" for the second one (unless you want to know the
       primary keys of temporary tables).

   foreign_key_info
         $sth = $dbh->foreign_key_info(undef, $pk_schema, $pk_table,
                                       undef, $fk_schema, $fk_table);

       Returns information about foreign key constraints, as specified in "foreign_key_info" in
       DBI, but with some limitations :

       •   information in rows returned by the $sth is incomplete with respect to the
           "foreign_key_info" in DBI specification. All requested fields are present, but the
           content is "undef" for some of them.

       The following nonempty fields are returned :

       PKTABLE_NAME: The primary (unique) key table identifier.

       PKCOLUMN_NAME: The primary (unique) key column identifier.

       FKTABLE_NAME: The foreign key table identifier.

       FKCOLUMN_NAME: The foreign key column identifier.

       KEY_SEQ: The column sequence number (starting with 1), when several columns belong to a
       same constraint.

       UPDATE_RULE: The referential action for the UPDATE rule.  The following codes are defined:

         CASCADE              0
         RESTRICT             1
         SET NULL             2
         NO ACTION            3
         SET DEFAULT          4

       Default is 3 ('NO ACTION').

       DELETE_RULE: The referential action for the DELETE rule.  The codes are the same as for
       UPDATE_RULE.

       DEFERRABILITY: The following codes are defined:

         INITIALLY DEFERRED   5
         INITIALLY IMMEDIATE  6
         NOT DEFERRABLE       7

       UNIQUE_OR_PRIMARY: Whether the column is primary or unique.

       Note: foreign key support in SQLite must be explicitly turned on through a "PRAGMA"
       command; see "Foreign keys" earlier in this manual.

   statistics_info
         $sth = $dbh->statistics_info(undef, $schema, $table,
                                       $unique_only, $quick);

       Returns information about a table and it's indexes, as specified in "statistics_info" in
       DBI, but with some limitations :

       •   information in rows returned by the $sth is incomplete with respect to the
           "statistics_info" in DBI specification. All requested fields are present, but the
           content is "undef" for some of them.

       The following nonempty fields are returned :

       TABLE_SCHEM: The name of the schema (database) that the table is in. The default schema is
       'main', temporary tables are in 'temp' and other databases will be in the name given when
       the database was attached.

       TABLE_NAME: The name of the table

       NON_UNIQUE: Contains 0 for unique indexes, 1 for non-unique indexes

       INDEX_NAME: The name of the index

       TYPE: SQLite uses 'btree' for all it's indexes

       ORDINAL_POSITION: Column sequence number (starting with 1).

       COLUMN_NAME: The name of the column

   ping
         my $bool = $dbh->ping;

       returns true if the database file exists (or the database is in-memory), and the database
       connection is active.

DRIVER PRIVATE METHODS

       The following methods can be called via the func() method with a little tweak, but the use
       of func() method is now discouraged by the DBI author for various reasons (see DBI's
       document
       <https://metacpan.org/pod/DBI::DBD#Using-install_method()-to-expose-driver-private-methods>
       for details). So, if you're using DBI >= 1.608, use these "sqlite_" methods. If you need
       to use an older DBI, you can call these like this:

         $dbh->func( ..., "(method name without sqlite_ prefix)" );

       Exception: "sqlite_trace" should always be called as is, even with func() method (to avoid
       conflict with DBI's trace() method).

         $dbh->func( ..., "sqlite_trace");

   $dbh->sqlite_last_insert_rowid()
       This method returns the last inserted rowid. If you specify an INTEGER PRIMARY KEY as the
       first column in your table, that is the column that is returned.  Otherwise, it is the
       hidden ROWID column. See the SQLite docs for details.

       Generally you should not be using this method. Use the DBI last_insert_id method instead.
       The usage of this is:

         $h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])

       Running "$h->last_insert_id("","","","")" is the equivalent of running
       "$dbh->sqlite_last_insert_rowid()" directly.

   $dbh->sqlite_db_filename()
       Retrieve the current (main) database filename. If the database is in-memory or temporary,
       this returns an empty string, or "undef".

   $dbh->sqlite_busy_timeout()
       Retrieve the current busy timeout.

   $dbh->sqlite_busy_timeout( $ms )
       Set the current busy timeout. The timeout is in milliseconds.

   $dbh->sqlite_create_function( $name, $argc, $code_ref, $flags )
       This method will register a new function which will be usable in an SQL query. The
       method's parameters are:

       $name
           The name of the function. This is the name of the function as it will be used from
           SQL.

       $argc
           The number of arguments taken by the function. If this number is -1, the function can
           take any number of arguments.

       $code_ref
           This should be a reference to the function's implementation.

       $flags
           You can optionally pass an extra flag bit to create_function, which then would be ORed
           with SQLITE_UTF8 (default). As of 1.47_02 (SQLite 3.8.9), only meaning bit is
           SQLITE_DETERMINISTIC (introduced at SQLite 3.8.3), which can make the function perform
           better. See C API documentation at <http://sqlite.org/c3ref/create_function.html> for
           details.

       For example, here is how to define a now() function which returns the current number of
       seconds since the epoch:

         $dbh->sqlite_create_function( 'now', 0, sub { return time } );

       After this, it could be used from SQL as:

         INSERT INTO mytable ( now() );

       The function should return a scalar value, and the value is treated as a text (or a number
       if appropriate) by default. If you do need to specify a type of the return value (like
       BLOB), you can return a reference to an array that contains the value and the type, as of
       1.65_01.

         $dbh->sqlite_create_function( 'md5', 1, sub { return [md5($_[0]), SQL_BLOB] } );

       REGEXP function

       SQLite includes syntactic support for an infix operator 'REGEXP', but without any
       implementation. The "DBD::SQLite" driver automatically registers an implementation that
       performs standard perl regular expression matching, using current locale. So for example
       you can search for words starting with an 'A' with a query like

         SELECT * from table WHERE column REGEXP '\bA\w+'

       If you want case-insensitive searching, use perl regex flags, like this :

         SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'

       The default REGEXP implementation can be overridden through the "create_function" API
       described above.

       Note that regexp matching will not use SQLite indices, but will iterate over all rows, so
       it could be quite costly in terms of performance.

   $dbh->sqlite_create_collation( $name, $code_ref )
       This method manually registers a new function which will be usable in an SQL query as a
       COLLATE option for sorting. Such functions can also be registered automatically on demand:
       see section "COLLATION FUNCTIONS" below.

       The method's parameters are:

       $name
           The name of the function exposed to SQL.

       $code_ref
           Reference to the function's implementation.  The driver will check that this is a
           proper sorting function.

   $dbh->sqlite_collation_needed( $code_ref )
       This method manually registers a callback function that will be invoked whenever an
       undefined collation sequence is required from an SQL statement. The callback is invoked as

         $code_ref->($dbh, $collation_name)

       and should register the desired collation using "sqlite_create_collation".

       An initial callback is already registered by "DBD::SQLite", so for most common cases it
       will be simpler to just add your collation sequences in the %DBD::SQLite::COLLATION hash
       (see section "COLLATION FUNCTIONS" below).

   $dbh->sqlite_create_aggregate( $name, $argc, $pkg, $flags )
       This method will register a new aggregate function which can then be used from SQL. The
       method's parameters are:

       $name
           The name of the aggregate function, this is the name under which the function will be
           available from SQL.

       $argc
           This is an integer which tells the SQL parser how many arguments the function takes.
           If that number is -1, the function can take any number of arguments.

       $pkg
           This is the package which implements the aggregator interface.

       $flags
           You can optionally pass an extra flag bit to create_aggregate, which then would be
           ORed with SQLITE_UTF8 (default). As of 1.47_02 (SQLite 3.8.9), only meaning bit is
           SQLITE_DETERMINISTIC (introduced at SQLite 3.8.3), which can make the function perform
           better. See C API documentation at <http://sqlite.org/c3ref/create_function.html> for
           details.

       The aggregator interface consists of defining three methods:

       new()
           This method will be called once to create an object which should be used to aggregate
           the rows in a particular group. The step() and finalize() methods will be called upon
           the reference return by the method.

       step(@_)
           This method will be called once for each row in the aggregate.

       finalize()
           This method will be called once all rows in the aggregate were processed and it should
           return the aggregate function's result. When there is no rows in the aggregate,
           finalize() will be called right after new().

       Here is a simple aggregate function which returns the variance (example adapted from
       pysqlite):

         package variance;

         sub new { bless [], shift; }

         sub step {
             my ( $self, $value ) = @_;

             push @$self, $value;
         }

         sub finalize {
             my $self = $_[0];

             my $n = @$self;

             # Variance is NULL unless there is more than one row
             return undef unless $n || $n == 1;

             my $mu = 0;
             foreach my $v ( @$self ) {
                 $mu += $v;
             }
             $mu /= $n;

             my $sigma = 0;
             foreach my $v ( @$self ) {
                 $sigma += ($v - $mu)**2;
             }
             $sigma = $sigma / ($n - 1);

             return $sigma;
         }

         $dbh->sqlite_create_aggregate( "variance", 1, 'variance' );

       The aggregate function can then be used as:

         SELECT group_name, variance(score)
         FROM results
         GROUP BY group_name;

       For more examples, see the DBD::SQLite::Cookbook.

   $dbh->sqlite_progress_handler( $n_opcodes, $code_ref )
       This method registers a handler to be invoked periodically during long running calls to
       SQLite.

       An example use for this interface is to keep a GUI updated during a large query. The
       parameters are:

       $n_opcodes
           The progress handler is invoked once for every $n_opcodes virtual machine opcodes in
           SQLite.

       $code_ref
           Reference to the handler subroutine.  If the progress handler returns non-zero, the
           SQLite operation is interrupted. This feature can be used to implement a "Cancel"
           button on a GUI dialog box.

           Set this argument to "undef" if you want to unregister a previous progress handler.

   $dbh->sqlite_commit_hook( $code_ref )
       This method registers a callback function to be invoked whenever a transaction is
       committed. Any callback set by a previous call to "sqlite_commit_hook" is overridden. A
       reference to the previous callback (if any) is returned.  Registering an "undef" disables
       the callback.

       When the commit hook callback returns zero, the commit operation is allowed to continue
       normally. If the callback returns non-zero, then the commit is converted into a rollback
       (in that case, any attempt to explicitly call "$dbh->rollback()" afterwards would yield an
       error).

   $dbh->sqlite_rollback_hook( $code_ref )
       This method registers a callback function to be invoked whenever a transaction is rolled
       back. Any callback set by a previous call to "sqlite_rollback_hook" is overridden. A
       reference to the previous callback (if any) is returned.  Registering an "undef" disables
       the callback.

   $dbh->sqlite_update_hook( $code_ref )
       This method registers a callback function to be invoked whenever a row is updated,
       inserted or deleted. Any callback set by a previous call to "sqlite_update_hook" is
       overridden. A reference to the previous callback (if any) is returned.  Registering an
       "undef" disables the callback.

       The callback will be called as

         $code_ref->($action_code, $database, $table, $rowid)

       where

       $action_code
           is an integer equal to either "DBD::SQLite::INSERT", "DBD::SQLite::DELETE" or
           "DBD::SQLite::UPDATE" (see "Action Codes");

       $database
           is the name of the database containing the affected row;

       $table
           is the name of the table containing the affected row;

       $rowid
           is the unique 64-bit signed integer key of the affected row within that table.

   $dbh->sqlite_set_authorizer( $code_ref )
       This method registers an authorizer callback to be invoked whenever SQL statements are
       being compiled by the "prepare" in DBI method.  The authorizer callback should return
       "DBD::SQLite::OK" to allow the action, "DBD::SQLite::IGNORE" to disallow the specific
       action but allow the SQL statement to continue to be compiled, or "DBD::SQLite::DENY" to
       cause the entire SQL statement to be rejected with an error. If the authorizer callback
       returns any other value, then "prepare" call that triggered the authorizer will fail with
       an error message.

       An authorizer is used when preparing SQL statements from an untrusted source, to ensure
       that the SQL statements do not try to access data they are not allowed to see, or that
       they do not try to execute malicious statements that damage the database. For example, an
       application may allow a user to enter arbitrary SQL queries for evaluation by a database.
       But the application does not want the user to be able to make arbitrary changes to the
       database. An authorizer could then be put in place while the user-entered SQL is being
       prepared that disallows everything except SELECT statements.

       The callback will be called as

         $code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)

       where

       $action_code
           is an integer that specifies what action is being authorized (see "Action Codes").

       $string1, $string2
           are strings that depend on the action code (see "Action Codes").

       $database
           is the name of the database ("main", "temp", etc.) if applicable.

       $trigger_or_view
           is the name of the inner-most trigger or view that is responsible for the access
           attempt, or "undef" if this access attempt is directly from top-level SQL code.

   $dbh->sqlite_backup_from_file( $filename )
       This method accesses the SQLite Online Backup API, and will take a backup of the named
       database file, copying it to, and overwriting, your current database connection. This can
       be particularly handy if your current connection is to the special :memory: database, and
       you wish to populate it from an existing DB.

   $dbh->sqlite_backup_to_file( $filename )
       This method accesses the SQLite Online Backup API, and will take a backup of the currently
       connected database, and write it out to the named file.

   $dbh->sqlite_backup_from_dbh( $another_dbh )
       This method accesses the SQLite Online Backup API, and will take a backup of the database
       for the passed handle, copying it to, and overwriting, your current database connection.
       This can be particularly handy if your current connection is to the special :memory:
       database, and you wish to populate it from an existing DB.  You can use this to backup
       from an in-memory database to another in-memory database.

   $dbh->sqlite_backup_to_dbh( $another_dbh )
       This method accesses the SQLite Online Backup API, and will take a backup of the currently
       connected database, and write it out to the passed database handle.

   $dbh->sqlite_enable_load_extension( $bool )
       Calling this method with a true value enables loading (external) SQLite3 extensions. After
       the call, you can load extensions like this:

         $dbh->sqlite_enable_load_extension(1);
         $sth = $dbh->prepare("select load_extension('libmemvfs.so')")
         or die "Cannot prepare: " . $dbh->errstr();

   $dbh->sqlite_load_extension( $file, $proc )
       Loading an extension by a select statement (with the "load_extension" SQLite3 function
       like above) has some limitations. If the extension you want to use creates other functions
       that are not native to SQLite, use this method instead. $file (a path to the extension) is
       mandatory, and $proc (an entry point name) is optional. You need to call
       "sqlite_enable_load_extension" before calling "sqlite_load_extension":

         $dbh->sqlite_enable_load_extension(1);
         $dbh->sqlite_load_extension('libsqlitefunctions.so')
         or die "Cannot load extension: " . $dbh->errstr();

       If the extension uses SQLite mutex functions like "sqlite3_mutex_enter", then the
       extension should be compiled with the same "SQLITE_THREADSAFE" compile-time setting as
       this module, see DBD::SQLite::compile_options().

   $dbh->sqlite_trace( $code_ref )
       This method registers a trace callback to be invoked whenever SQL statements are being
       run.

       The callback will be called as

         $code_ref->($statement)

       where

       $statement
           is a UTF-8 rendering of the SQL statement text as the statement first begins
           executing.

       Additional callbacks might occur as each triggered subprogram is entered. The callbacks
       for triggers contain a UTF-8 SQL comment that identifies the trigger.

       See also "TRACING" in DBI for better tracing options.

   $dbh->sqlite_profile( $code_ref )
       This method registers a profile callback to be invoked whenever a SQL statement finishes.

       The callback will be called as

         $code_ref->($statement, $elapsed_time)

       where

       $statement
           is the original statement text (without bind parameters).

       $elapsed_time
           is an estimate of wall-clock time of how long that statement took to run (in
           milliseconds).

       This method is considered experimental and is subject to change in future versions of
       SQLite.

       See also DBI::Profile for better profiling options.

   $dbh->sqlite_table_column_metadata( $dbname, $tablename, $columnname )
       is for internal use only.

   $dbh->sqlite_db_status()
       Returns a hash reference that holds a set of status information of database connection
       such as cache usage. See <https://www.sqlite.org/c3ref/c_dbstatus_options.html> for
       details. You may also pass 0 as an argument to reset the status.

   $sth->sqlite_st_status()
       Returns a hash reference that holds a set of status information of SQLite statement handle
       such as full table scan count. See
       <https://www.sqlite.org/c3ref/c_stmtstatus_counter.html> for details. Statement status
       only holds the current value.

         my $status = $sth->sqlite_st_status();
         my $cur = $status->{fullscan_step};

       You may also pass 0 as an argument to reset the status.

   $dbh->sqlite_db_config( $id, $new_integer_value )
       You can change how the connected database should behave like this:

         use DBD::SQLite::Constants qw/:database_connection_configuration_options/;

         my $dbh = DBI->connect('dbi:SQLite::memory:');

         # This disables language features that allow ordinary SQL
         # to deliberately corrupt the database file
         $dbh->sqlite_db_config( SQLITE_DBCONFIG_DEFENSIVE, 1 );

         # This disables two-arg version of fts3_tokenizer.
         $dbh->sqlite_db_config( SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER, 0 );

       "sqlite_db_config" returns the new value after the call. If you just want to know the
       current value without changing anything, pass a negative integer value.

         my $current_value = $dbh->sqlite_db_config( SQLITE_DBCONFIG_DEFENSIVE, -1 );

       As of this writing, "sqlite_db_config" only supports options that set an integer value.
       "SQLITE_DBCONFIG_LOOKASIDE" and "SQLITE_DBCONFIG_MAINDBNAME" are not supported. See also
       "https://www.sqlite.org/capi3ref.html#sqlite3_db_config" for details.

   $dbh->sqlite_create_module()
       Registers a name for a virtual table module. Module names must be registered before
       creating a new virtual table using the module and before using a preexisting virtual table
       for the module.  Virtual tables are explained in DBD::SQLite::VirtualTable.

   $dbh->sqlite_limit( $category_id, $new_value )
       Sets a new run-time limit for the category, and returns the current limit.  If the new
       value is a negative number (or omitted), the limit is unchanged and just returns the
       current limit. Category ids (SQLITE_LIMIT_LENGTH, SQLITE_LIMIT_VARIABLE_NUMBER, etc) can
       be imported from DBD::SQLite::Constants.

   $dbh->sqlite_get_autocommit()
       Returns true if the internal SQLite connection is in an autocommit mode.  This does not
       always return the same value as "$dbh->{AutoCommit}".  This returns false if you
       explicitly issue a "<BEGIN"> statement.

   $dbh->sqlite_txn_state()
       Returns the internal transaction status of SQLite (not of DBI).  Return values
       (SQLITE_TXN_NONE, SQLITE_TXN_READ, SQLITE_TXN_WRITE) can be imported from
       DBD::SQLite::Constants. You may pass an optional schema name (usually "main"). If SQLite
       does not support this function, or if you pass a wrong schema name, -1 is returned.

   $dbh->sqlite_error_offset()
       Returns the byte offset of the start of a problematic input SQL token or -1 if the most
       recent error does not reference a specific token in the input SQL (or DBD::SQLite is built
       with an older version of SQLite).

DRIVER FUNCTIONS

   DBD::SQLite::compile_options()
       Returns an array of compile options (available since SQLite 3.6.23, bundled in DBD::SQLite
       1.30_01), or an empty array if the bundled library is old or compiled with
       SQLITE_OMIT_COMPILEOPTION_DIAGS.

   DBD::SQLite::sqlite_status()
       Returns a hash reference that holds a set of status information of SQLite runtime such as
       memory usage or page cache usage (see
       <https://www.sqlite.org/c3ref/c_status_malloc_count.html> for details). Each of the entry
       contains the current value and the highwater value.

         my $status = DBD::SQLite::sqlite_status();
         my $cur  = $status->{memory_used}{current};
         my $high = $status->{memory_used}{highwater};

       You may also pass 0 as an argument to reset the status.

   DBD::SQLite::strlike($pattern, $string, $escape_char), DBD::SQLite::strglob($pattern, $string)
       As of 1.49_05 (SQLite 3.10.0), you can use these two functions to see if a string matches
       a pattern. These may be useful when you create a virtual table or a custom function.  See
       <http://sqlite.org/c3ref/strlike.html> and <http://sqlite.org/c3ref/strglob.html> for
       details.

DRIVER CONSTANTS

       A subset of SQLite C constants are made available to Perl, because they may be needed when
       writing hooks or authorizer callbacks. For accessing such constants, the "DBD::SQLite"
       module must be explicitly "use"d at compile time. For example, an authorizer that forbids
       any DELETE operation would be written as follows :

         use DBD::SQLite;
         $dbh->sqlite_set_authorizer(sub {
           my $action_code = shift;
           return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
                                                      : DBD::SQLite::OK;
         });

       The list of constants implemented in "DBD::SQLite" is given below; more information can be
       found ad at <https://www.sqlite.org/c3ref/constlist.html>.

   Authorizer Return Codes
         OK
         DENY
         IGNORE

   Action Codes
       The "set_authorizer" method registers a callback function that is invoked to authorize
       certain SQL statement actions. The first parameter to the callback is an integer code that
       specifies what action is being authorized. The second and third parameters to the callback
       are strings, the meaning of which varies according to the action code. Below is the list
       of action codes, together with their associated strings.

         # constant              string1         string2
         # ========              =======         =======
         CREATE_INDEX            Index Name      Table Name
         CREATE_TABLE            Table Name      undef
         CREATE_TEMP_INDEX       Index Name      Table Name
         CREATE_TEMP_TABLE       Table Name      undef
         CREATE_TEMP_TRIGGER     Trigger Name    Table Name
         CREATE_TEMP_VIEW        View Name       undef
         CREATE_TRIGGER          Trigger Name    Table Name
         CREATE_VIEW             View Name       undef
         DELETE                  Table Name      undef
         DROP_INDEX              Index Name      Table Name
         DROP_TABLE              Table Name      undef
         DROP_TEMP_INDEX         Index Name      Table Name
         DROP_TEMP_TABLE         Table Name      undef
         DROP_TEMP_TRIGGER       Trigger Name    Table Name
         DROP_TEMP_VIEW          View Name       undef
         DROP_TRIGGER            Trigger Name    Table Name
         DROP_VIEW               View Name       undef
         INSERT                  Table Name      undef
         PRAGMA                  Pragma Name     1st arg or undef
         READ                    Table Name      Column Name
         SELECT                  undef           undef
         TRANSACTION             Operation       undef
         UPDATE                  Table Name      Column Name
         ATTACH                  Filename        undef
         DETACH                  Database Name   undef
         ALTER_TABLE             Database Name   Table Name
         REINDEX                 Index Name      undef
         ANALYZE                 Table Name      undef
         CREATE_VTABLE           Table Name      Module Name
         DROP_VTABLE             Table Name      Module Name
         FUNCTION                undef           Function Name
         SAVEPOINT               Operation       Savepoint Name

COLLATION FUNCTIONS

   Definition
       SQLite v3 provides the ability for users to supply arbitrary comparison functions, known
       as user-defined "collation sequences" or "collating functions", to be used for comparing
       two text values.  <https://www.sqlite.org/datatype3.html#collation> explains how
       collations are used in various SQL expressions.

   Builtin collation sequences
       The following collation sequences are builtin within SQLite :

       BINARY
           Compares string data using memcmp(), regardless of text encoding.

       NOCASE
           The same as binary, except the 26 upper case characters of ASCII are folded to their
           lower case equivalents before the comparison is performed. Note that only ASCII
           characters are case folded. SQLite does not attempt to do full UTF case folding due to
           the size of the tables required.

       RTRIM
           The same as binary, except that trailing space characters are ignored.

       In addition, "DBD::SQLite" automatically installs the following collation sequences :

       perl
           corresponds to the Perl "cmp" operator

       perllocale
           Perl "cmp" operator, in a context where "use locale" is activated.

   Usage
       You can write for example

         CREATE TABLE foo(
             txt1 COLLATE perl,
             txt2 COLLATE perllocale,
             txt3 COLLATE nocase
         )

       or

         SELECT * FROM foo ORDER BY name COLLATE perllocale

   Unicode handling
       Depending on the "$dbh->{sqlite_string_mode}" value, strings coming from the database and
       passed to the collation function may be decoded as UTF-8. This only works, though, if the
       "sqlite_string_mode" attribute is set before the first call to a perl collation sequence.
       The recommended way to activate unicode is to set "sqlite_string_mode" at connection time:

         my $dbh = DBI->connect(
             "dbi:SQLite:dbname=foo", "", "",
             {
                 RaiseError         => 1,
                 sqlite_string_mode => DBD_SQLITE_STRING_MODE_UNICODE_STRICT,
             }
         );

   Adding user-defined collations
       The native SQLite API for adding user-defined collations is exposed through methods
       "sqlite_create_collation" and "sqlite_collation_needed".

       To avoid calling these functions every time a $dbh handle is created, "DBD::SQLite" offers
       a simpler interface through the %DBD::SQLite::COLLATION hash : just insert your own
       collation functions in that hash, and whenever an unknown collation name is encountered in
       SQL, the appropriate collation function will be loaded on demand from the hash. For
       example, here is a way to sort text values regardless of their accented characters :

         use DBD::SQLite;
         $DBD::SQLite::COLLATION{no_accents} = sub {
           my ( $a, $b ) = map lc, @_;
           tr[àâáäåãçðèêéëìîíïñòôóöõøùûúüý]
             [aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
           $a cmp $b;
         };
         my $dbh  = DBI->connect("dbi:SQLite:dbname=dbfile");
         my $sql  = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
         my $rows = $dbh->selectall_arrayref($sql);

       The builtin "perl" or "perllocale" collations are predefined in that same hash.

       The COLLATION hash is a global registry within the current process; hence there is a risk
       of undesired side-effects. Therefore, to prevent action at distance, the hash is
       implemented as a "write-only" hash, that will happily accept new entries, but will raise
       an exception if any attempt is made to override or delete a existing entry (including the
       builtin "perl" and "perllocale").

       If you really, really need to change or delete an entry, you can always grab the tied
       object underneath %DBD::SQLite::COLLATION --- but don't do that unless you really know
       what you are doing. Also observe that changes in the global hash will not modify existing
       collations in existing database handles: it will only affect new requests for collations.
       In other words, if you want to change the behaviour of a collation within an existing
       $dbh, you need to call the "create_collation" method directly.

FULLTEXT SEARCH

       SQLite is bundled with an extension module for full-text indexing. Tables with this
       feature enabled can be efficiently queried to find rows that contain one or more instances
       of some specified words, in any column, even if the table contains many large documents.

       Explanations for using this feature are provided in a separate document: see
       DBD::SQLite::Fulltext_search.

R* TREE SUPPORT

       The RTREE extension module within SQLite adds support for creating a R-Tree, a special
       index for range and multidimensional queries.  This allows users to create tables that can
       be loaded with (as an example) geospatial data such as latitude/longitude coordinates for
       buildings within a city :

         CREATE VIRTUAL TABLE city_buildings USING rtree(
            id,               -- Integer primary key
            minLong, maxLong, -- Minimum and maximum longitude
            minLat, maxLat    -- Minimum and maximum latitude
         );

       then query which buildings overlap or are contained within a specified region:

         # IDs that are contained within query coordinates
         my $contained_sql = <<"";
         SELECT id FROM city_buildings
            WHERE  minLong >= ? AND maxLong <= ?
            AND    minLat  >= ? AND maxLat  <= ?

         # ... and those that overlap query coordinates
         my $overlap_sql = <<"";
         SELECT id FROM city_buildings
            WHERE    maxLong >= ? AND minLong <= ?
            AND      maxLat  >= ? AND minLat  <= ?

         my $contained = $dbh->selectcol_arrayref($contained_sql,undef,
                               $minLong, $maxLong, $minLat, $maxLat);

         my $overlapping = $dbh->selectcol_arrayref($overlap_sql,undef,
                               $minLong, $maxLong, $minLat, $maxLat);

       For more detail, please see the SQLite R-Tree page (<https://www.sqlite.org/rtree.html>).
       Note that custom R-Tree queries using callbacks, as mentioned in the prior link, have not
       been implemented yet.

VIRTUAL TABLES IMPLEMENTED IN PERL

       SQLite has a concept of "virtual tables" which look like regular tables but are
       implemented internally through specific functions.  The fulltext or R* tree features
       described in the previous chapters are examples of such virtual tables, implemented in C
       code.

       "DBD::SQLite" also supports virtual tables implemented in Perl code: see
       DBD::SQLite::VirtualTable for using or implementing such virtual tables. These can have
       many interesting uses for joining regular DBMS data with some other kind of data within
       your Perl programs. Bundled with the present distribution are :

       •   DBD::SQLite::VirtualTable::FileContent : implements a virtual column that exposes file
           contents. This is especially useful in conjunction with a fulltext index; see
           DBD::SQLite::Fulltext_search.

       •   DBD::SQLite::VirtualTable::PerlData : binds to a Perl array within the Perl program.
           This can be used for simple import/export operations, for debugging purposes, for
           joining data from different sources, etc.

       Other Perl virtual tables may also be published separately on CPAN.

FOR DBD::SQLITE EXTENSION AUTHORS

       Since 1.30_01, you can retrieve the bundled SQLite C source and/or header like this:

         use File::ShareDir 'dist_dir';
         use File::Spec::Functions 'catfile';

         # the whole sqlite3.h header
         my $sqlite3_h = catfile(dist_dir('DBD-SQLite'), 'sqlite3.h');

         # or only a particular header, amalgamated in sqlite3.c
         my $what_i_want = 'parse.h';
         my $sqlite3_c = catfile(dist_dir('DBD-SQLite'), 'sqlite3.c');
         open my $fh, '<', $sqlite3_c or die $!;
         my $code = do { local $/; <$fh> };
         my ($parse_h) = $code =~ m{(
           /\*+[ ]Begin[ ]file[ ]$what_i_want[ ]\*+
           .+?
           /\*+[ ]End[ ]of[ ]$what_i_want[ ]\*+/
         )}sx;
         open my $out, '>', $what_i_want or die $!;
         print $out $parse_h;
         close $out;

       You usually want to use this in your extension's "Makefile.PL", and you may want to add
       DBD::SQLite to your extension's "CONFIGURE_REQUIRES" to ensure your extension users use
       the same C source/header they use to build DBD::SQLite itself (instead of the ones
       installed in their system).

TO DO

       The following items remain to be done.

   Leak Detection
       Implement one or more leak detection tests that only run during AUTOMATED_TESTING and
       RELEASE_TESTING and validate that none of the C code we work with leaks.

   Stream API for Blobs
       Reading/writing into blobs using "sqlite2_blob_open" / "sqlite2_blob_close".

   Support for custom callbacks for R-Tree queries
       Custom queries of a R-Tree index using a callback are possible with the SQLite C API
       (<https://www.sqlite.org/rtree.html>), so one could potentially use a callback that
       narrowed the result set down based on a specific need, such as querying for overlapping
       circles.

SUPPORT

       Bugs should be reported to GitHub issues:

       <https://github.com/DBD-SQLite/DBD-SQLite/issues>

       or via RT if you prefer:

       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite>

       Note that bugs of bundled SQLite library (i.e. bugs in "sqlite3.[ch]") should be reported
       to the SQLite developers at sqlite.org via their bug tracker or via their mailing list.

       The master repository is on GitHub:

       <https://github.com/DBD-SQLite/DBD-SQLite>.

       We also have a mailing list:

       <http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbd-sqlite>

AUTHORS

       Matt Sergeant <matt@sergeant.org>

       Francis J. Lacoste <flacoste@logreport.org>

       Wolfgang Sourdeau <wolfgang@logreport.org>

       Adam Kennedy <adamk@cpan.org>

       Max Maischein <corion@cpan.org>

       Laurent Dami <dami@cpan.org>

       Kenichi Ishigaki <ishigaki@cpan.org>

COPYRIGHT

       The bundled SQLite code in this distribution is Public Domain.

       DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.

       Some parts copyright 2008 Francis J. Lacoste.

       Some parts copyright 2008 Wolfgang Sourdeau.

       Some parts copyright 2008 - 2013 Adam Kennedy.

       Some parts copyright 2009 - 2013 Kenichi Ishigaki.

       Some parts derived from DBD::SQLite::Amalgamation copyright 2008 Audrey Tang.

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       The full text of the license can be found in the LICENSE file included with this module.