Provided by: mysql-cluster-client-5.1_7.0.9-1ubuntu7_i386
mysql - the MySQL command-line tool
mysql [options] db_name
mysql is a simple SQL shell (with GNU readline capabilities). It
supports interactive and noninteractive use. When used interactively,
query results are presented in an ASCII-table format. When used
noninteractively (for example, as a filter), the result is presented in
tab-separated format. The output format can be changed using command
If you have problems due to insufficient memory for large result sets,
use the --quick option. This forces mysql to retrieve results from the
server a row at a time rather than retrieving the entire result set and
buffering it in memory before displaying it. This is done by returning
the result set using the mysql_use_result() C API function in the
client/server library rather than mysql_store_result().
Using mysql is very easy. Invoke it from the prompt of your command
interpreter as follows:
shell> mysql db_name
shell> mysql --user=user_name --password=your_password db_name
Then type an SQL statement, end it with “;”, \g, or \G and press Enter.
As of MySQL 5.1.10, typing Control-C causes mysql to attempt to kill
the current statement. If this cannot be done, or Control-C is typed
again before the statement is killed, mysql exits. Previously,
Control-C caused mysql to exit in all cases.
You can execute SQL statements in a script file (batch file) like this:
shell> mysql db_name < script.sql > output.tab
mysql supports the options in the following list. It also reads option
files and supports the options for processing them described at
Section 220.127.116.11.1, “Command-Line Options that Affect Option-File
· --help, -?
Display a help message and exit.
Enable automatic rehashing. This option is on by default, which
enables database, table, and column name completion. Use
--disable-auto-rehash to disable rehashing. That causes mysql to
start faster, but you must issue the rehash command if you want to
use name completion.
To complete a name, enter the first part and press Tab. If the name
is unambiguous, mysql completes it. Otherwise, you can press Tab
again to see the possible names that begin with what you have typed
so far. Completion does not occur if there is no default database.
· --batch, -B
Print results using tab as the column separator, with each row on a
new line. With this option, mysql does not use the history file.
Batch mode results in nontabular output format and escaping of
special characters. Escaping may be disabled by using raw mode; see
the description for the --raw option.
The directory where character sets are installed. See Section 9.2,
“The Character Set Used for Data and Sorting”.
Write column names in results.
· --column-type-info, -m
Display result set metadata. This option was added in MySQL 5.1.14.
(Before that, use --debug-info.) The -m short option was added in
· --comments, -c
Whether to preserve comments in statements sent to the server. The
default is --skip-comments (discard comments), enable with
--comments (preserve comments). This option was added in MySQL
· --compress, -C
Compress all information sent between the client and the server if
both support compression.
· --database=db_name, -D db_name
The database to use. This is useful primarily in an option file.
· --debug[=debug_options], -# [debug_options]
Write a debugging log. A typical debug_options string is
´d:t:o,file_name´. The default is ´d:t:o,/tmp/mysql.trace´.
Print some debugging information when the program exits. This
option was added in MySQL 5.1.21.
· --debug-info, -T
Before MySQL 5.1.14, this option prints debugging information and
memory and CPU usage statistics when the program exits, and also
causes display of result set metadata during execution. As of MySQL
5.1.14, use --column-type-info to display result set metadata.
Use charset_name as the default character set for the client and
A common issue that can occur when the operating system uses utf8
or another multi-byte character set is that output from the mysql
client is formatted incorrectly, due to the fact that the MySQL
client uses the latin1 character set by default. You can usually
fix such issues by using this option to force the client to use the
system character set instead.
See Section 9.2, “The Character Set Used for Data and Sorting”, for
Set the statement delimiter. The default is the semicolon character
Disable named commands. Use the \* form only, or use named commands
only at the beginning of a line ending with a semicolon (“;”).
mysql starts with this option enabled by default. However, even
with this option, long-format commands still work from the first
line. See the section called “MYSQL COMMANDS”.
· --execute=statement, -e statement
Execute the statement and quit. The default output format is like
that produced with --batch. See Section 18.104.22.168, “Using Options on
the Command Line”, for some examples.
· --force, -f
Continue even if an SQL error occurs.
· --host=host_name, -h host_name
Connect to the MySQL server on the given host.
· --html, -H
Produce HTML output.
· --ignore-spaces, -i
Ignore spaces after function names. The effect of this is described
in the discussion for the IGNORE_SPACE SQL mode (see Section 5.1.8,
“Server SQL Modes”).
Write line numbers for errors. Disable this with
Enable or disable LOCAL capability for LOAD DATA INFILE. With no
value, the option enables LOCAL. The option may be given as
--local-infile=0 or --local-infile=1 to explicitly disable or
enable LOCAL. Enabling LOCAL has no effect if the server does not
also support it.
· --named-commands, -G
Enable named mysql commands. Long-format commands are allowed, not
just short-format commands. For example, quit and \q both are
recognized. Use --skip-named-commands to disable named commands.
See the section called “MYSQL COMMANDS”.
· --no-auto-rehash, -A
Deprecated form of -skip-auto-rehash. Use --disable-auto-rehash
instead. See the description for --auto-rehash.
· --no-beep, -b
Do not beep when errors occur.
· --no-named-commands, -g
Deprecated, use --disable-named-commands instead.
Deprecated form of --skip-pager. See the --pager option.
Do not copy output to a file. the section called “MYSQL COMMANDS”,
discusses tee files further.
· --one-database, -o
Ignore statements except those for the default database named on
the command line. This is useful for skipping updates to other
databases in the binary log.
Use the given command for paging query output. If the command is
omitted, the default pager is the value of your PAGER environment
variable. Valid pagers are less, more, cat [> filename], and so
forth. This option works only on Unix and only in interactive mode.
To disable paging, use --skip-pager. the section called “MYSQL
COMMANDS”, discusses output paging further.
· --password[=password], -p[password]
The password to use when connecting to the server. If you use the
short option form (-p), you cannot have a space between the option
and the password. If you omit the password value following the
--password or -p option on the command line, you are prompted for
Specifying a password on the command line should be considered
insecure. See Section 22.214.171.124, “End-User Guidelines for Password
· --pipe, -W
On Windows, connect to the server via a named pipe. This option
applies only for connections to a local server, and only if the
server supports named-pipe connections.
· --port=port_num, -P port_num
The TCP/IP port number to use for the connection.
Set the prompt to the specified format. The default is mysql>. The
special sequences that the prompt can contain are described in the
section called “MYSQL COMMANDS”.
The connection protocol to use for connecting to the server. It is
useful when the other connection parameters normally would cause a
protocol to be used other than the one you want. For details on the
allowable values, see Section 4.2.2, “Connecting to the MySQL
· --quick, -q
Do not cache each query result, print each row as it is received.
This may slow down the server if the output is suspended. With this
option, mysql does not use the history file.
· --raw, -r
For tabular output, the “boxing” around columns enables one column
value to be distinguished from another. For nontabular output (such
as is produced in batch mode or when the --batch or --silent option
is given), special characters are escaped in the output so they can
be identified easily. Newline, tab, NUL, and backslash are written
as \n, \t, \0, and \\. The --raw option disables this character
The following example demonstrates tabular versus nontabular output
and the use of raw mode to disable escaping:
mysql> SELECT CHAR(92);
| CHAR(92) |
| \ |
% mysql -s
mysql> SELECT CHAR(92);
% mysql -s -r
mysql> SELECT CHAR(92);
If the connection to the server is lost, automatically try to
reconnect. A single reconnect attempt is made each time the
connection is lost. To suppress reconnection behavior, use
· --safe-updates, --i-am-a-dummy, -U
Allow only those UPDATE and DELETE statements that specify which
rows to modify by using key values. If you have set this option in
an option file, you can override it by using --safe-updates on the
command line. See the section called “MYSQL TIPS”, for more
information about this option.
Do not send passwords to the server in old (pre-4.1.1) format. This
prevents connections except for servers that use the newer password
Cause warnings to be shown after each statement if there are any.
This option applies to interactive and batch mode.
Ignore SIGINT signals (typically the result of typing Control-C).
· --silent, -s
Silent mode. Produce less output. This option can be given multiple
times to produce less and less output.
This option results in nontabular output format and escaping of
special characters. Escaping may be disabled by using raw mode; see
the description for the --raw option.
· --skip-column-names, -N
Do not write column names in results. The short format, -N is
deprecated, use the long format instead.
· --skip-line-numbers, -L
Do not write line numbers for errors. Useful when you want to
compare result files that include error messages. The short format,
-L is deprecated, use the long format instead.
· --socket=path, -S path
For connections to localhost, the Unix socket file to use, or, on
Windows, the name of the named pipe to use.
Options that begin with --ssl specify whether to connect to the
server via SSL and indicate where to find SSL keys and
certificates. See Section 126.96.36.199, “SSL Command Options”.
· --table, -t
Display output in table format. This is the default for interactive
use, but can be used to produce table output in batch mode.
Append a copy of output to the given file. This option works only
in interactive mode. the section called “MYSQL COMMANDS”,
discusses tee files further.
· --unbuffered, -n
Flush the buffer after each query.
· --user=user_name, -u user_name
The MySQL user name to use when connecting to the server.
· --verbose, -v
Verbose mode. Produce more output about what the program does. This
option can be given multiple times to produce more and more output.
(For example, -v -v -v produces table output format even in batch
· --version, -V
Display version information and exit.
· --vertical, -E
Print query output rows vertically (one line per column value).
Without this option, you can specify vertical output for individual
statements by terminating them with \G.
· --wait, -w
If the connection cannot be established, wait and retry instead of
· --xml, -X
Produce XML output.
Prior to MySQL 5.1.12, there was no differentiation in the
output when using this option between columns containing the
NULL value and columns containing the string literal ´NULL´;
both were represented as
Beginning with MySQL 5.1.12, the output when --xml is used with
mysql matches that of mysqldump --xml. See mysqldump(1) for
Beginning with MySQL 5.1.18, the XML output also uses an XML
namespace, as shown here:
shell> mysql --xml -uroot -e "SHOW VARIABLES LIKE ´version%´"
<resultset statement="SHOW VARIABLES LIKE ´version%´" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<field name="Value">Source distribution</field>
You can also set the following variables by using --var_name=value. The
--set-variable format is deprecated.
The number of seconds before connection timeout. (Default value is
The maximum packet length to send to or receive from the server.
(Default value is 16MB.)
The automatic limit for rows in a join when using --safe-updates.
(Default value is 1,000,000.)
The buffer size for TCP/IP and socket communication. (Default value
The automatic limit for SELECT statements when using
--safe-updates. (Default value is 1,000.)
On Unix, the mysql client writes a record of executed statements to a
history file. By default, this file is named .mysql_history and is
created in your home directory. To specify a different file, set the
value of the MYSQL_HISTFILE environment variable.
The .mysql_history should be protected with a restrictive access mode
because sensitive information might be written to it, such as the text
of SQL statements that contain passwords. See Section 188.8.131.52, “End-
User Guidelines for Password Security”.
If you do not want to maintain a history file, first remove
.mysql_history if it exists, and then use either of the following
· Set the MYSQL_HISTFILE variable to /dev/null. To cause this setting
to take effect each time you log in, put the setting in one of your
shell´s startup files.
· Create .mysql_history as a symbolic link to /dev/null:
shell> ln -s /dev/null $HOME/.mysql_history
You need do this only once.
mysql sends each SQL statement that you issue to the server to be
executed. There is also a set of commands that mysql itself interprets.
For a list of these commands, type help or \h at the mysql> prompt:
List of all MySQL commands:
Note that all text commands must be first on line and end with ´;´
? (\?) Synonym for ‘help´.
clear (\c) Clear command.
connect (\r) Reconnect to the server. Optional arguments are db and host.
delimiter (\d) Set statement delimiter.
edit (\e) Edit command with $EDITOR.
ego (\G) Send command to mysql server, display result vertically.
exit (\q) Exit mysql. Same as quit.
go (\g) Send command to mysql server.
help (\h) Display this help.
nopager (\n) Disable pager, print to stdout.
notee (\t) Don´t write into outfile.
pager (\P) Set PAGER [to_pager]. Print the query results via PAGER.
print (\p) Print current command.
prompt (\R) Change your mysql prompt.
quit (\q) Quit mysql.
rehash (\#) Rebuild completion hash.
source (\.) Execute an SQL script file. Takes a file name as an argument.
status (\s) Get status information from the server.
system (\!) Execute a system shell command.
tee (\T) Set outfile [to_outfile]. Append everything into given
use (\u) Use another database. Takes database name as argument.
charset (\C) Switch to another charset. Might be needed for processing
binlog with multi-byte charsets.
warnings (\W) Show warnings after every statement.
nowarning (\w) Don´t show warnings after every statement.
For server side help, type ´help contents´
Each command has both a long and short form. The long form is not case
sensitive; the short form is. The long form can be followed by an
optional semicolon terminator, but the short form should not.
The use of short-form commands within multi-line /* ... */ comments is
· help [arg], \h [arg], \? [arg], ? [arg]
Display a help message listing the available mysql commands.
If you provide an argument to the help command, mysql uses it as a
search string to access server-side help from the contents of the
MySQL Reference Manual. For more information, see the section
called “MYSQL SERVER-SIDE HELP”.
· charset charset_name, \C charset_name
Change the default character set and issue a SET NAMES statement.
This enables the character set to remain synchronized on the client
and server if mysql is run with auto-reconnect enabled (which is
not recommended), because the specified character set is used for
reconnects. This command was added in MySQL 5.1.7.
· clear, \c
Clear the current input. Use this if you change your mind about
executing the statement that you are entering.
· connect [db_name host_name]], \r [db_name host_name]]
Reconnect to the server. The optional database name and host name
arguments may be given to specify the default database or the host
where the server is running. If omitted, the current values are
· delimiter str, \d str
Change the string that mysql interprets as the separator between
SQL statements. The default is the semicolon character (“;”).
The delimiter can be specified as an unquoted or quoted argument.
Quoting can be done with either single quote (´) or douple quote
(") characters. To include a quote within a quoted string, either
quote the string with the other quote character or escape the quote
with a backslash (“\”) character. Backslash should be avoided
outside of quoted strings because it is the escape character for
MySQL. For an unquoted argument, the delmiter is read up to the
first space or end of line. For a quoted argument, the delimiter is
read up to the matching quote on the line.
When the delimiter recognized by mysql is set to something other
than the default of “;”, instances of that character are sent to
the server without interpretation. However, the server itself still
interprets “;” as a statement delimiter and processes statements
accordingly. This behavior on the server side comes into play for
multiple-statement execution (see Section 21.9.12, “C API Support
for Multiple Statement Execution”), and for parsing the body of
stored procedures and functions, triggers, and events (see
Section 19.1, “Defining Stored Programs”).
· edit, \e
Edit the current input statement. mysql checks the values of the
EDITOR and VISUAL environment variables to determine which editor
to use. The default editor is vi if neither variable is set.
The edit command works only in Unix.
· ego, \G
Send the current statement to the server to be executed and display
the result using vertical format.
· exit, \q
· go, \g
Send the current statement to the server to be executed.
· nopager, \n
Disable output paging. See the description for pager.
The nopager command works only in Unix.
· notee, \t
Disable output copying to the tee file. See the description for
· nowarning, \w
Enable display of warnings after each statement.
· pager [command], \P [command]
Enable output paging. By using the --pager option when you invoke
mysql, it is possible to browse or search query results in
interactive mode with Unix programs such as less, more, or any
other similar program. If you specify no value for the option,
mysql checks the value of the PAGER environment variable and sets
the pager to that. Pager functionality works only in interactive
Output paging can be enabled interactively with the pager command
and disabled with nopager. The command takes an optional argument;
if given, the paging program is set to that. With no argument, the
pager is set to the pager that was set on the command line, or
stdout if no pager was specified.
Output paging works only in Unix because it uses the popen()
function, which does not exist on Windows. For Windows, the tee
option can be used instead to save query output, although it is not
as convenient as pager for browsing output in some situations.
· print, \p
Print the current input statement without executing it.
· prompt [str], \R [str]
Reconfigure the mysql prompt to the given string. The special
character sequences that can be used in the prompt are described
later in this section.
If you specify the prompt command with no argument, mysql resets
the prompt to the default of mysql>.
· quit, \q
· rehash, \#
Rebuild the completion hash that enables database, table, and
column name completion while you are entering statements. (See the
description for the --auto-rehash option.)
· source file_name, \. file_name
Read the named file and executes the statements contained therein.
On Windows, you can specify path name separators as / or \\.
· status, \s
Provide status information about the connection and the server you
are using. If you are running in --safe-updates mode, status also
prints the values for the mysql variables that affect your queries.
· system command, \! command
Execute the given command using your default command interpreter.
The system command works only in Unix.
· tee [file_name], \T [file_name]
By using the --tee option when you invoke mysql, you can log
statements and their output. All the data displayed on the screen
is appended into a given file. This can be very useful for
debugging purposes also. mysql flushes results to the file after
each statement, just before it prints its next prompt. Tee
functionality works only in interactive mode.
You can enable this feature interactively with the tee command.
Without a parameter, the previous file is used. The tee file can be
disabled with the notee command. Executing tee again re-enables
· use db_name, \u db_name
Use db_name as the default database.
· warnings, \W
Enable display of warnings after each statement (if there are any).
Here are a few tips about the pager command:
· You can use it to write to a file and the results go only to the
mysql> pager cat > /tmp/log.txt
You can also pass any options for the program that you want to use
as your pager:
mysql> pager less -n -i -S
· In the preceding example, note the -S option. You may find it very
useful for browsing wide query results. Sometimes a very wide
result set is difficult to read on the screen. The -S option to
less can make the result set much more readable because you can
scroll it horizontally using the left-arrow and right-arrow keys.
You can also use -S interactively within less to switch the
horizontal-browse mode on and off. For more information, read the
less manual page:
shell> man less
· The -F and -X options may be used with less to cause it to exit if
output fits on one screen, which is convenient when no scrolling is
mysql> pager less -n -i -S -F -X
· You can specify very complex pager commands for handling query
mysql> pager cat | tee /dr1/tmp/res.txt \
| tee /dr2/tmp/res2.txt | less -n -i -S
In this example, the command would send query results to two files
in two different directories on two different file systems mounted
on /dr1 and /dr2, yet still display the results onscreen via less.
You can also combine the tee and pager functions. Have a tee file
enabled and pager set to less, and you are able to browse the results
using the less program and still have everything appended into a file
the same time. The difference between the Unix tee used with the pager
command and the mysql built-in tee command is that the built-in tee
works even if you do not have the Unix tee available. The built-in tee
also logs everything that is printed on the screen, whereas the Unix
tee used with pager does not log quite that much. Additionally, tee
file logging can be turned on and off interactively from within mysql.
This is useful when you want to log some queries to a file, but not
The prompt command reconfigures the default mysql> prompt. The string
for defining the prompt can contain the following special sequences.
|Option | Description |
|\c | A counter that increments |
| | for each statement you |
| | issue |
|\D | The full current date |
|\d | The default database |
|\h | The server host |
|\l | The current delimiter (new |
| | in 5.1.12) |
|\m | Minutes of the current |
| | time |
|\n | A newline character |
|\O | The current month in |
| | three-letter format (Jan, |
| | Feb, ...) |
|\o | The current month in |
| | numeric format |
|\P | am/pm |
|\p | The current TCP/IP port or |
| | socket file |
|\R | The current time, in |
| | 24-hour military time |
| | (0–23) |
|\r | The current time, standard |
| | 12-hour time (1–12) |
|\S | Semicolon |
|\s | Seconds of the current |
| | time |
|\t | A tab character |
|\U | |
| | Your full |
| | user_name@host_name |
| | account name |
|\u | Your user name |
|\v | The server version |
|\w | The current day of the |
| | week in three-letter |
| | format (Mon, Tue, ...) |
|\Y | The current year, four |
| | digits |
|\y | The current year, two |
| | digits |
|\_ | A space |
|\ | A space (a space follows |
| | the backslash) |
|\´ | Single quote |
|\" | Double quote |
|\\ | A literal “\” backslash |
| | character |
|\x | |
| | x, for any “x” not |
| | listed above |
You can set the prompt in several ways:
· Use an environment variable. You can set the MYSQL_PS1 environment
variable to a prompt string. For example:
shell> export MYSQL_PS1="(\u@\h) [\d]> "
· Use a command-line option. You can set the --prompt option on the
command line to mysql. For example:
shell> mysql --prompt="(\u@\h) [\d]> "
· Use an option file. You can set the prompt option in the [mysql]
group of any MySQL option file, such as /etc/my.cnf or the .my.cnf
file in your home directory. For example:
In this example, note that the backslashes are doubled. If you set
the prompt using the prompt option in an option file, it is
advisable to double the backslashes when using the special prompt
options. There is some overlap in the set of allowable prompt
options and the set of special escape sequences that are recognized
in option files. (The rules for escape sequences in option files
are listed in Section 184.108.40.206, “Using Option Files”.) The overlap
may cause you problems if you use single backslashes. For example,
\s is interpreted as a space rather than as the current seconds
value. The following example shows how to define a prompt within an
option file to include the current time in HH:MM:SS> format:
· Set the prompt interactively. You can change your prompt
interactively by using the prompt (or \R) command. For example:
mysql> prompt (\u@\h) [\d]>\_
PROMPT set to ´(\u@\h) [\d]>\_´
(user@host) [database]> prompt
Returning to default PROMPT of mysql>
MYSQL SERVER-SIDE HELP
mysql> help search_string
If you provide an argument to the help command, mysql uses it as a
search string to access server-side help from the contents of the MySQL
Reference Manual. The proper operation of this command requires that
the help tables in the mysql database be initialized with help topic
information (see Section 5.1.9, “Server-Side Help”).
If there is no match for the search string, the search fails:
mysql> help me
Please try to run ´help contents´ for a list of all accessible topics
Use help contents to see a list of the help categories:
mysql> help contents
You asked for help about help category: "Contents"
For more information, type ´help <item>´, where <item> is one of the
Functions and Modifiers for Use with GROUP BY
If the search string matches multiple items, mysql shows a list of
mysql> help logs
Many help items for your request exist.
To make a more specific request, please type ´help <item>´,
where <item> is one of the following topics:
SHOW BINARY LOGS
Use a topic as the search string to see the help entry for that topic:
mysql> help show binary logs
Name: ´SHOW BINARY LOGS´
SHOW BINARY LOGS
SHOW MASTER LOGS
Lists the binary log files on the server. This statement is used as
part of the procedure described in [purge-binary-logs], that shows how
to determine which logs can be purged.
mysql> SHOW BINARY LOGS;
| Log_name | File_size |
| binlog.000015 | 724935 |
| binlog.000016 | 733481 |
EXECUTING SQL STATEMENTS FROM A TEXT FILE
The mysql client typically is used interactively, like this:
shell> mysql db_name
However, it is also possible to put your SQL statements in a file and
then tell mysql to read its input from that file. To do so, create a
text file text_file that contains the statements you wish to execute.
Then invoke mysql as shown here:
shell> mysql db_name < text_file
If you place a USE db_name statement as the first statement in the
file, it is unnecessary to specify the database name on the command
shell> mysql < text_file
If you are already running mysql, you can execute an SQL script file
using the source command or \. command:
mysql> source file_name
mysql> \. file_name
Sometimes you may want your script to display progress information to
the user. For this you can insert statements like this:
SELECT ´<info_to_display>´ AS ´ ´;
The statement shown outputs <info_to_display>.
You can also invoke mysql with the --verbose option, which causes each
statement to be displayed before the result that it produces.
As of MySQL 5.1.23, mysql ignores Unicode byte order mark (BOM)
characters at the beginning of input files. Previously, it read them
and sent them to the server, resulting in a syntax error. Presence of a
BOM does not cause mysql to change its default character set. To do
that, invoke mysql with an option such as --default-character-set=utf8.
For more information about batch mode, see Section 3.5, “Using mysql in
This section describes some techniques that can help you use mysql more
Displaying Query Results Vertically
Some query results are much more readable when displayed vertically,
instead of in the usual horizontal table format. Queries can be
displayed vertically by terminating the query with \G instead of a
semicolon. For example, longer text values that include newlines often
are much easier to read with vertical output:
mysql> SELECT * FROM mails WHERE LENGTH(txt) < 300 LIMIT 300,1\G
*************************** 1. row ***************************
date: 2000-03-01 23:29:50
mail_to: "Thimble Smith" <firstname.lastname@example.org>
txt: >>>>> "Thimble" == Thimble Smith writes:
Thimble> Hi. I think this is a good idea. Is anyone familiar
Thimble> with UTF-8 or Unicode? Otherwise, I´ll put this on my
Thimble> TODO list and see what happens.
Yes, please do that.
1 row in set (0.09 sec)
Using the --safe-updates Option
For beginners, a useful startup option is --safe-updates (or
--i-am-a-dummy, which has the same effect). It is helpful for cases
when you might have issued a DELETE FROM tbl_name statement but
forgotten the WHERE clause. Normally, such a statement deletes all rows
from the table. With --safe-updates, you can delete rows only by
specifying the key values that identify them. This helps prevent
When you use the --safe-updates option, mysql issues the following
statement when it connects to the MySQL server:
SET sql_safe_updates=1, sql_select_limit=1000, sql_max_join_size=1000000;
See Section 5.1.5, “Session System Variables”.
The SET statement has the following effects:
· You are not allowed to execute an UPDATE or DELETE statement unless
you specify a key constraint in the WHERE clause or provide a LIMIT
clause (or both). For example:
UPDATE tbl_name SET not_key_column=val WHERE key_column=val;
UPDATE tbl_name SET not_key_column=val LIMIT 1;
· The server limits all large SELECT results to 1,000 rows unless the
statement includes a LIMIT clause.
· The server aborts multiple-table SELECT statements that probably
need to examine more than 1,000,000 row combinations.
To specify limits different from 1,000 and 1,000,000, you can override
the defaults by using the --select_limit and --max_join_size options:
shell> mysql --safe-updates --select_limit=500 --max_join_size=10000
Disabling mysql Auto-Reconnect
If the mysql client loses its connection to the server while sending a
statement, it immediately and automatically tries to reconnect once to
the server and send the statement again. However, even if mysql
succeeds in reconnecting, your first connection has ended and all your
previous session objects and settings are lost: temporary tables, the
autocommit mode, and user-defined and session variables. Also, any
current transaction rolls back. This behavior may be dangerous for you,
as in the following example where the server was shut down and
restarted between the first and second statements without you knowing
mysql> SET @a=1;
Query OK, 0 rows affected (0.05 sec)
mysql> INSERT INTO t VALUES(@a);
ERROR 2006: MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 1
Current database: test
Query OK, 1 row affected (1.30 sec)
mysql> SELECT * FROM t;
| a |
| NULL |
1 row in set (0.05 sec)
The @a user variable has been lost with the connection, and after the
reconnection it is undefined. If it is important to have mysql
terminate with an error if the connection has been lost, you can start
the mysql client with the --skip-reconnect option.
For more information about auto-reconnect and its effect on state
information when a reconnection occurs, see Section 21.9.11,
“Controlling Automatic Reconnection Behavior”.
Copyright 2007-2008 MySQL AB, 2009 Sun Microsystems, Inc.
This documentation is free software; you can redistribute it and/or
modify it only under the terms of the GNU General Public License as
published by the Free Software Foundation; version 2 of the License.
This documentation is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along
with the program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA or see
For more information, please refer to the MySQL Reference Manual, which
may already be installed locally and which is also available online at
Sun Microsystems, Inc. (http://www.mysql.com/).