mysql - Unix, Linux Command

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 options.


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


Or:





shell> mysql --user=user_name --password=your_password db_name


Then type an SQL statement, end it with
\(lq;\(rq,
\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


On Unix, the
mysql
client writes a record of executed statements to a history file. See
the section called \(lqMYSQL HISTORY FILE\(rq.


mysql
supports the following options, which can be specified on the command line or in the
[mysql]
and
[client]
option file groups.
mysql
also supports the options for processing option files described at
Section 4.2.3.3.1, \(lqCommand-Line Options that Affect Option-File Handling\(rq.



o





Display a help message and exit.



o





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.



o





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.



o





On a computer having multiple network interfaces, this option can be used to select which interface is employed when connecting to the MySQL server.


This option is supported only in the version of the
mysql
client that is supplied with MySQL Cluster, beginning with MySQL Cluster NDB 6.3.4. It is not available in standard MySQL 5.1 releases.



o





The directory where character sets are installed. See
Section 9.5, \(lqCharacter Set Configuration\(rq.



o





Write column names in results.



o





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 MySQL 5.1.21.



o





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 5.1.23.



o





Compress all information sent between the client and the server if both support compression.



o





The database to use. This is useful primarily in an option file.



o





Write a debugging log. A typical
debug_options
string is
'd:t:o,file_name'. The default is
'd:t:o,/tmp/mysql.trace'.



o





Print some debugging information when the program exits. This option was added in MySQL 5.1.21.



o





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.



o





Use
charset_name
as the default character set for the client and connection.


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 9.5, \(lqCharacter Set Configuration\(rq, for more information.



o





Set the statement delimiter. The default is the semicolon character (\(lq;\(rq).



o





Disable named commands. Use the
\*
form only, or use named commands only at the beginning of a line ending with a semicolon (\(lq;\(rq).
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 \(lqMYSQL COMMANDS\(rq.



o





Execute the statement and quit. The default output format is like that produced with
--batch. See
Section 4.2.3.1, \(lqUsing Options on the Command Line\(rq, for some examples. With this option,
mysql
does not use the history file.



o





Continue even if an SQL error occurs.



o





Connect to the MySQL server on the given host.



o





Produce HTML output.



o





Ignore spaces after function names. The effect of this is described in the discussion for the
IGNORE_SPACE
SQL mode (see
Section 5.1.7, \(lqServer SQL Modes\(rq).



o





Write line numbers for errors. Disable this with
--skip-line-numbers.



o





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.



o





Enable named
mysql
commands. Long-format commands are permitted, 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 \(lqMYSQL COMMANDS\(rq.



o





This has the same effect as
-skip-auto-rehash. See the description for
--auto-rehash.



o





Do not beep when errors occur.



o





Deprecated, use
--disable-named-commands
instead.
--no-named-commands
is removed in MySQL 5.5.



o





Deprecated form of
--skip-pager. See the
--pager
option.
--no-pager
is removed in MySQL 5.5.



o





Deprecated form of
--skip-tee. See the
--tee
option.
--no-tee
is removed in MySQL 5.5.



o





Ignore statements except those that occur while the default database is the one named on the command line. This option is rudimentary and should be used with care. Statement filtering is based only on
USE
statements.


Initially,
mysql
executes statements in the input because specifying a database
db_name
on the command line is equivalent to inserting
USE db_name
at the beginning of the input. Then, for each
USE
statement encountered,
mysql
accepts or rejects following statements depending on whether the database named is the one on the command line. The content of the statements is immaterial.


Suppose that
mysql
is invoked to process this set of statements:




DELETE FROM db2.t2;
USE db2;
DROP TABLE db1.t1;
CREATE TABLE db1.t1 (i INT);
USE db1;
INSERT INTO t1 (i) VALUES(1);
CREATE TABLE db2.t1 (j INT);


If the command line is
mysql --force --one-database db1,
mysql
handles the input as follows:















o





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 \(lqMYSQL COMMANDS\(rq, discusses output paging further.



o





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,
mysql
prompts for one.


Specifying a password on the command line should be considered insecure. See
Section 5.3.2.2, \(lqEnd-User Guidelines for Password Security\(rq. You can use an option file to avoid giving the password on the command line.



o





On Windows, connect to the server using a named pipe. This option applies only if the server supports named-pipe connections.



o





The TCP/IP port number to use for the connection.



o





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 \(lqMYSQL COMMANDS\(rq.



o





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 permissible values, see
Section 4.2.2, \(lqConnecting to the MySQL Server\(rq.



o





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.



o





For tabular output, the
\(lqboxing\(rq
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 escaping.


The following example demonstrates tabular versus nontabular output and the use of raw mode to disable escaping:




% mysql
mysql> SELECT CHAR(92);
+----------+
| CHAR(92) |
+----------+
| \        |
+----------+
% mysql -s
mysql> SELECT CHAR(92);
CHAR(92)
\\
% mysql -s -r
mysql> SELECT CHAR(92);
CHAR(92)
\



o





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
--skip-reconnect.



o





Permit 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 \(lqMYSQL TIPS\(rq, for more information about this option.



o





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 format.



o





Cause warnings to be shown after each statement if there are any. This option applies to interactive and batch mode.



o





Ignore
SIGINT
signals (typically the result of typing Control-C).



o





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.



o





Do not write column names in results.



o





Do not write line numbers for errors. Useful when you want to compare result files that include error messages.



o





For connections to
localhost, the Unix socket file to use, or, on Windows, the name of the named pipe to use.



o





Options that begin with
--ssl
specify whether to connect to the server using SSL and indicate where to find SSL keys and certificates. See
Section 5.5.6.3, \(lqSSL Command Options\(rq.



o





Display output in table format. This is the default for interactive use, but can be used to produce table output in batch mode.



o





Append a copy of output to the given file. This option works only in interactive mode.
the section called \(lqMYSQL COMMANDS\(rq, discusses tee files further.



o





Flush the buffer after each query.



o





The MySQL user name to use when connecting to the server.



o





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 mode.)



o





Display version information and exit.



o





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.



o





If the connection cannot be established, wait and retry instead of aborting.



o





Produce XML output.










<field name="column_name">NULL</field>


Beginning with MySQL 5.1.12, the output when
--xml
is used with
mysql
matches that of
mysqldump --xml. See
mysqldump(1)
for details.


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%'"
<?xml version="1.0"?>
<resultset statement="SHOW VARIABLES LIKE 'version%'" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<row>
<field name="Variable_name">version</field>
<field name="Value">5.0.40-debug</field>
</row>
<row>
<field name="Variable_name">version_comment</field>
<field name="Value">Source distribution</field>
</row>
<row>
<field name="Variable_name">version_compile_machine</field>
<field name="Value">i686</field>
</row>
<row>
<field name="Variable_name">version_compile_os</field>
<field name="Value">suse-linux-gnu</field>
</row>
</resultset>


(See
\m[blue]Bug#25946\m[][1].)


You can also set the following variables by using
--var_name=value. The
--set-variable
format is deprecated and is removed in MySQL 5.5.



o





The number of seconds before connection timeout. (Default value is
0.)



o





The maximum packet length to send to or receive from the server. (Default value is 16MB.)



o





The automatic limit for rows in a join when using
--safe-updates. (Default value is 1,000,000.)



o





The buffer size for TCP/IP and socket communication. (Default value is 16KB.)



o





The automatic limit for
SELECT
statements when using
--safe-updates. (Default value is 1,000.)


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:





mysql> help
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
               outfile.
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 not supported.



o





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 \(lqMYSQL SERVER-SIDE HELP\(rq.



o





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.



o





Clear the current input. Use this if you change your mind about executing the statement that you are entering.



o





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 used.



o





Change the string that
mysql
interprets as the separator between SQL statements. The default is the semicolon character (\(lq;\(rq).


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 (\(lq\\(rq) 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
\(lq;\(rq, instances of that character are sent to the server without interpretation. However, the server itself still interprets
\(lq;\(rq
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, \(lqC API Support for Multiple Statement Execution\(rq), and for parsing the body of stored procedures and functions, triggers, and events (see
Section 19.1, \(lqDefining Stored Programs\(rq).


Be careful about defining a delimiter that might occur within other words. For example, if you define the delimiter as
X, you will be unable to use the word
INDEX
in statements.



o





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.



o





Send the current statement to the server to be executed and display the result using vertical format.



o





Exit
mysql.



o





Send the current statement to the server to be executed.



o





Disable output paging. See the description for
pager.


The
nopager
command works only in Unix.



o





Disable output copying to the tee file. See the description for
tee.



o





Enable display of warnings after each statement.



o





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 mode.


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.



o





Print the current input statement without executing it.



o





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>.



o





Exit
mysql.



o





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.)



o





Read the named file and executes the statements contained therein. On Windows, you can specify path name separators as
/
or
\\.



o





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.



o





Execute the given command using your default command interpreter.


The
system
command works only in Unix.



o





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 logging.



o





Use
db_name
as the default database.



o





Enable display of warnings after each statement (if there are any).


Here are a few tips about the
pager
command:



o







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



o







shell> man less



o







mysql> pager less -n -i -S -F -X



o







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 using
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 others.


The
prompt
command reconfigures the default
mysql>
prompt. The string for defining the prompt can contain the following special sequences.




You can set the prompt in several ways:



o







shell> export MYSQL_PS1="(\u@\h) [\d]> "



o







shell> mysql --prompt="(\u@\h) [\d]> "
(user@host) [database]>



o







[mysql]
prompt=(\\u@\\h) [\\d]>\\_


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 permissible 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 4.2.3.3, \(lqUsing Option Files\(rq.) 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:




[mysql]
prompt="\\r:\\m:\\s> "



o







mysql> prompt (\u@\h) [\d]>\_
PROMPT set to '(\u@\h) [\d]>\_'
(user@host) [database]>
(user@host) [database]> prompt
Returning to default PROMPT of mysql>
mysql>


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 5.3.2.2, \(lqEnd-User Guidelines for Password Security\(rq.


It is possible to suppress logging of statements to the history file by using the
--batch
or
--execute
option.


If you do not want to maintain a history file, first remove
.mysql_history
if it exists, and then use either of the following techniques:



o






o







shell> ln -s /dev/null $HOME/.mysql_history


You need do this only once.





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 5.1.8, \(lqServer-Side Help\(rq).


If there is no match for the search string, the search fails:





mysql> help me
Nothing found
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
following categories:
   Account Management
   Administration
   Data Definition
   Data Manipulation
   Data Types
   Functions
   Functions and Modifiers for Use with GROUP BY
   Geographic Features
   Language Structure
   Plugins
   Storage Engines
   Stored Routines
   Table Maintenance
   Transactions
   Triggers


If the search string matches multiple items,
mysql
shows a list of matching topics:





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
   SHOW BINARY LOGS
   SHOW ENGINE
   SHOW 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'
Description:
Syntax:
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 |
+---------------+-----------+


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 line:





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, \(lqUsing mysql in Batch Mode\(rq.


This section describes some techniques that can help you use
mysql
more effectively.


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 ***************************
  msg_nro: 3068
     date: 2000-03-01 23:29:50
time_zone: +0200
mail_from: Monty
    reply: monty@no.spam.com
  mail_to: "Thimble Smith" <tim@no.spam.com>
      sbj: UTF-8
      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.
Regards,
Monty
     file: inbox-jani-1
     hash: 190402944
1 row in set (0.09 sec)


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 accidents.


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 5.1.4, \(lqServer System Variables\(rq.


The
SET
statement has the following effects:



o







UPDATE tbl_name SET not_key_column=val WHERE key_column=val;
UPDATE tbl_name SET not_key_column=val LIMIT 1;



o






o





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


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 it:





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, \(lqControlling Automatic Reconnection Behavior\(rq.


Copyright © 1997, 2011, Oracle and/or its affiliates. All rights reserved.


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 http://www.gnu.org/licenses/.




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