Provided by: libsql-statement-perl_1.412-1_all bug


       SQL::Statement::Structure - parse and examine structure of SQL queries


           use SQL::Statement;
           my $sql    = "SELECT a FROM b JOIN c WHERE c=? AND e=7 ORDER BY f DESC LIMIT 5,2";
           my $parser = SQL::Parser->new();
           $parser->parse("LOAD 'MyLib::MySyntax' ");
           my $stmt = SQL::Statement->new($sql,$parser);
           printf "Command             %s\n",$stmt->command;
           printf "Num of Placeholders %s\n",scalar $stmt->params;
           printf "Columns             %s\n",join( ',', map {$_->name} $stmt->column_defs() );
           printf "Tables              %s\n",join( ',', map {$_->name} $stmt->tables() );
           printf "Where operator      %s\n",join( ',', $stmt->where->op() );
           printf "Limit               %s\n",$stmt->limit();
           printf "Offset              %s\n",$stmt->offset();

           # these will work not before $stmt->execute()
           printf "Order Columns       %s\n",join(',', map {$_->column} $stmt->order() );


       The SQL::Statement module can be used by itself, without DBI and without a subclass to
       parse SQL statements and to allow you to examine the structure of the statement (table
       names, column names, where clause predicates, etc.).  It will also execute statements
       using in-memory tables.  That means that you can create and populate some tables, then
       query them and fetch the results of the queries as well as examine the differences between
       statement metadata during different phases of prepare, execute, fetch. See the remainder
       of this document for a description of how to create and modify a parser object and how to
       use it to parse and examine SQL statements.  See SQL::Statement for other uses of the

Creating a parser object

       The parser object only needs to be created once per script. It can then be reused to parse
       any number of SQL statements. The basic creation of a parser is this:

           my $parser = SQL::Parser->new();

       You can set the error-reporting for the parser the same way you do in DBI:

           $parser->{RaiseError}=1;   # turn on die-on-error behaviour
           $parser->{PrinteError}=1;  # turn on warnings-on-error behaviour

       As with DBI, RaiseError defaults to 0 (off) and PrintError defaults to 1 (on).

       For many purposes, the built-in SQL syntax should be sufficient. However, if you need to,
       you can change the behaviour of the parser by extending the supported SQL syntax either by
       loading a file containing definitions; or by issuing SQL commands that modify the way the
       parser treats types, keywords, functions, and operators.

           $parser->parse("LOAD MyLib::MySyntax");
           $parser->parse("CREATE TYPE myDataType");

       See SQL::Statement::Syntax for details of the supported SQL syntax and for methods of
       extending the syntax.

Parsing SQL statements

       While you only need to define a new SQL::Parser object once per script, you need to define
       a new SQL::Statment object once for each statement you want to parse.

           my $stmt = SQL::Statement->new($sql, $parser);

       The call to new() takes two arguments - the SQL string you want to parse, and the
       SQL::Parser object you previously created.  The call to new is the equivalent of a DBI
       call to prepare() - it parses the SQL into a structure but does not attempt to execute the
       SQL unless you explicitly call execute().

Examining the structure of SQL statements

       The following methods can be used to obtain information about a query:

       Returns the SQL command. See SQL::Statement::Syntax for supported command. Example:

           my $command = $stmt->command();

   column definitions
           my $numColumns = $stmt->column_defs();  # Scalar context
           my @columnList = $stmt->column_defs();  # Array context
           my($col1, $col2) = ($stmt->column_defs(0), $stmt->column_defs(1));

       This method is used to retrieve column lists. The meaning depends on the query command:

           SELECT $col1, $col2, ... $colN FROM $table WHERE ...
           UPDATE $table SET $col1 = $val1, $col2 = $val2, ...
               $colN = $valN WHERE ...
           INSERT INTO $table ($col1, $col2, ..., $colN) VALUES (...)

       When used without arguments, the method returns a list of the columns $col1, $col2, ...,
       $colN, you may alternatively use a column number as argument. Note that the column list
       may be empty as in

           INSERT INTO $table VALUES (...)

       and in CREATE or DROP statements.

       But what does "returning a column" mean? It is returning an "SQL::Statement::Util::Column"
       instance, a class that implements the methods "table" and "name", both returning the
       respective scalar. For example, consider the following statements:

           INSERT INTO foo (bar) VALUES (1)
           SELECT bar FROM foo WHERE ...
           SELECT FROM foo WHERE ...

       In all these cases exactly one column instance would be returned with

           $col->name() eq 'bar'
           $col->table() eq 'foo'

           my $tableNum = $stmt->tables();  # Scalar context
           my @tables = $stmt->tables();    # Array context
           my($table1, $table2) = ($stmt->tables(0), $stmt->tables(1));

       Similar to "columns", this method returns instances of "SQL::Statement::Table". For
       UPDATE, DELETE, INSERT, CREATE and DROP, a single table will always be returned.  SELECT
       statements can return more than one table, in case of joins. Table objects offer a single
       method, "name" which returns the table name.

           my $paramNum = $stmt->params();  # Scalar context
           my @params = $stmt->params();    # Array context
           my($p1, $p2) = ($stmt->params(0), $stmt->params(1));

       The "params" method returns information about the input parameters used in a statement.
       For example, consider the following:

           INSERT INTO foo VALUES (?, ?)

       This would return two instances of "SQL::Statement::Param". Param objects implement a
       single method, "$param-"num()>, which retrieves the parameter number. (0 and 1, in the
       above example). As of now, not very useful ... :-)

           my $rowValueNum = $stmt->row_values(); # Scalar context
           my @rowValues = $stmt->row_values(0);  # Array context
           my($rval1, $rval2) = ($stmt->row_values(0,0),

       This method is used for statements like

           UPDATE $table SET $col1 = $val1, $col2 = $val2, ...
               $colN = $valN WHERE ...
           INSERT INTO $table (...) VALUES ($val1, $val2, ..., $valN),
                                           ($val1, $val2, ..., $valN)

       to read the values $val1, $val2, ... $valN. It returns (lists of) scalar values or
       "SQL::Statement::Param" instances.

           my $orderNum = $stmt->order();   # Scalar context
           my @order = $stmt->order();      # Array context
           my($o1, $o2) = ($stmt->order(0), $stmt->order(1));

       In SELECT statements you can use this for looking at the ORDER clause.  Example:

           SELECT * FROM FOO ORDER BY id DESC, name

       In this case, "order" could return 2 instances of "SQL::Statement::Order".  You can use
       the methods "$o->table()", "$o->column()", "$o->direction()" and "$o->desc()" to examine
       the order object.

           my $limit = $stmt->limit();

       In a SELECT statement you can use a "LIMIT" clause to implement cursoring:

           SELECT * FROM FOO LIMIT 5
           SELECT * FROM FOO LIMIT 5, 5
           SELECT * FROM FOO LIMIT 10, 5

       These three statements would retrieve the rows 0..4, 5..9, 10..14 of the table FOO,
       respectively. If no "LIMIT" clause is used, then the method "$stmt->limit" returns undef.
       Otherwise it returns the limit number (the maximum number of rows) from the statement (5
       or 10 for the statements above).

           my $offset = $stmt->offset();

       If no "LIMIT" clause is used, then the method "$stmt->limit" returns undef. Otherwise it
       returns the offset number (the index of the first row to be included in the limit clause).

           my $where_hash = $stmt->where_hash();

       To manually evaluate the WHERE clause, fetch the topmost where clause node with the
       "where_hash" method. Then evaluate the left-hand and right-hand side of the operation,
       perhaps recursively. Once that is done, apply the operator and finally negate the result,
       if required.

       The where clause nodes have (up to) 4 attributes:

       op          contains the operator, one of "AND", "OR", "=", "<>", ">=", ">", "<=", "<",
                   "LIKE", "CLIKE", "IS", "IN", "BETWEEN" or a user defined operator, if any.

       arg1        contains the left-hand side of the operator. This can be a scalar value, a
                   hash containing column or function definition, a parameter definition (hash
                   has attribute "type" defined) or another operation (hash has attribute "op"

       arg2        contains the right-hand side of the operator. This can be a scalar value, a
                   hash containing column or function definition, a parameter definition (hash
                   has attribute "type" defined) or another operation (hash has attribute "op"

       neg         contains a TRUE value, if the operation result must be negated after

       To illustrate the above, consider the following WHERE clause:

           WHERE NOT (id > 2 AND name = 'joe') OR name IS NULL

       We can represent this clause by the following tree:

                     (id > 2)   (name = 'joe')
                            \   /
                 NOT         AND
                                \      (name IS NULL)
                                 \    /

       Thus the WHERE clause would return an SQL::Statement::Op instance with the op() field set
       to 'OR'. The arg2() field would return another SQL::Statement::Op instance with arg1()
       being the SQL::Statement::Column instance representing id, the arg2() field containing the
       value undef (NULL) and the op() field being 'IS'.

       The arg1() field of the topmost Op instance would return an Op instance with op() eq 'AND'
       and neg() returning TRUE. The arg1() and arg2() fields would be Op's representing "id > 2"
       and "name = 'joe'".

       Of course there's a ready-for-use method for WHERE clause evaluation:

       The WHERE clause evaluation depends on an object being used for fetching parameter and
       column values. Usually this can be an SQL::Statement::RAM::Table object or SQL::Eval
       object, but in fact it can be any object that supplies the methods

           $val = $eval->param($paramNum);
           $val = $eval->column($table, $column);

       Once you have such an object, you can call eval_where;

           $match = $stmt->eval_where($eval);

           my $where = $stmt->where();

       This method is used to examine the syntax tree of the "WHERE" clause. It returns undef (if
       no "WHERE" clause was used) or an instance of SQL::Statement::Term.

       The where clause is evaluated automatically on the current selected row of the table
       currently worked on when it's "value()" method is invoked.

       "SQL::Statement" creates the object tree for where clause evaluation directly after
       successfully parsing a statement from the given "where_clause", if any.

Executing and fetching data from SQL statements

       When called from a DBD or other subclass of SQL::Statement, the execute() method will be
       executed against whatever datasource (persistent storage) is supplied by the DBD or the
       subclass (e.g. CSV files for DBD::CSV, or BerkeleyDB for DBD::DBM). If you are using
       SQL::Statement directly rather than as a subclass, you can call the execute() method and
       the statements will be executed() using temporary in-memory tables. When used directly,
       like that, you need to create a cache hashref and pass it as the first argument to

         my $cache  = {};
         my $parser = SQL::Parser->new();
         my $stmt   = SQL::Statement->new('CREATE TABLE x (id INT)',$parser);
         $stmt->execute( $cache );

       If you are using a statement with placeholders, those can be passed to execute after the

         $stmt      = SQL::Statement->new('INSERT INTO y VALUES(?,?)',$parser);
         $stmt->execute( $cache, 7, 'foo' );

       Only a single "fetch()" method is provided - it returns a single row of data as an
       arrayref. Use a loop to fetch all rows:

        while (my $row = $stmt->fetch()) {
            # ...

   an example of executing and fetching
        #!/usr/bin/perl -w
        use strict;
        use SQL::Statement;

        my $cache={};
        my $parser = SQL::Parser->new();
        for my $sql(split /\n/,
        "  CREATE TABLE a (b INT)
           INSERT INTO a VALUES(1)
           INSERT INTO a VALUES(2)
           SELECT MAX(b) FROM a  "
           $stmt = SQL::Statement->new($sql,$parser);
           next unless $stmt->command eq 'SELECT';
           while (my $row=$stmt->fetch)
               print "@$row\n";


       Copyright (c) 2005, Jeff Zucker <>, all rights reserved.  Copyright (c)
       2009, Jens Rehsack <>, all rights reserved.

       This document may be freely modified and distributed under the same terms as Perl itself.