mysql - the MariaDB command-line tool
mysql [options] db_name
mysql is a simple SQL shell (with GNU readline capabilities). It supports interactive and non-interactive use. When used interactively, query results are presented in an ASCII-table format. When used non-interactively (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
shell> mysql --user=user_name --password=your_password db_name
Then type an SQL statement, end it with “;”, \g, or \G and press Enter.
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.
You can execute SQL statements in a script file (batch file) like this:
shell> mysql db_name < script.sql > output.tab
mysql supports the following options, which can be specified on the command line or in the [mysql], [client], [client-server] or [client-mariadb] option file groups. mysql also supports the options for processing option files.
• --help, -?, -I
Display a help message and exit.
Abort ’source filename’ operations in case of errors.
Enable automatic rehashing. This option is on by default, which enables database, table, and column name completion. Use --disable-auto-rehash, --no-auto-rehash, or --skip-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.
Automatically switch to vertical output mode if the result is wider than the terminal width.
• --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.
Binary mode allows certain character sequences to be processed as data that would otherwise be treated with a special meaning by the parser. Specifically, this switch turns off parsing of all client commands except \C and DELIMITER in non-interactive mode (i.e., when binary mode is combined with either 1) piped input, 2) the --batch mysql option, or 3) the ’source’ command). Also, in binary mode, occurrences of ’\r\n’ and ASCII ’\0’ are preserved within strings, whereas by default, ’\r\n’ is translated to ’\n’ and ’\0’ is disallowed in user input.
The directory where character sets are installed.
Write column names in results.
• --column-type-info, -m
Display result set metadata.
• --comments, -c
Whether to preserve comments in statements sent to the server. The default is --skip-comments (discard comments), enable with --comments (preserve comments).
• --compress, -C
Compress all information sent between the client and the server if both support compression.
Set the number of seconds before connection timeout. (Default value is 0.)
• --database=db_name, -D db_name
The database to use.
• --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.
• --debug-info, -T
Prints debugging information and memory and CPU usage statistics when the program exits.
Default authentication client-side plugin to use.
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 MariaDB 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.
Set filename as the file to read default options from after the global defaults files has been read. Must be given as first option.
Set filename as the file to read default options from, override global defaults files. Must be given as first option.
In addition to the groups named on the command line, read groups that have the given suffix.
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. Disables --force and history file. The default output format is like that produced with --batch.
• --force, -f
Continue even if an SQL error occurs. Sets --abort-source-on-error to 0.
• --host=host_name, -h host_name
Connect to the MariaDB server on the given host.
• --html, -H
Produce HTML output.
• --ignore-spaces, -i
Ignore spaces after function names. Allows one to have spaces (including tab characters and new line characters) between function name and ’(’. The drawback is that this causes built in functions to become reserved words.
SQL Command to execute when connecting to the MariaDB server. Will automatically be re-executed when reconnecting.
Write line numbers for errors. Disable this with --skip-line-numbers.
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.
Set the maximum packet length to send to or receive from the server. (Default value is 16MB, largest 1GB.)
Set the automatic limit for rows in a join when using --safe-updates. (Default value is 1,000,000.)
• --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”. Disabled by default.
Set the buffer size for TCP/IP and socket communication. (Default value is 16KB.)
• --no-auto-rehash, -A
This has the same effect as --skip-auto-rehash. See the description for --auto-rehash.
• --no-beep, -b
Do not beep when errors occur.
Do not read default options from any option file. This must be given as the first argument.
• --one-database, -o
Ignore statements except those those that occur while the default database is the one named on the command line. This filtering is limited, and based only on USE statements. 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, mysql prompts for one.
Specifying a password on the command line should be considered insecure. You can use an option file to avoid giving the password on the command line.
• --pipe, -W
On Windows, connect to the server via a named pipe. This option applies only if the server supports named-pipe connections.
Directory for client-side plugins.
• --port=port_num, -P port_num
The TCP/IP port number to use for the connection or 0 for default to, in order of preference, my.cnf, $MYSQL_TCP_PORT, /etc/services, built-in default (3306). Forces --protocol=tcp when specified on the command line without other connection properties.
Print the program argument list and exit. This must be given as the first argument.
Get progress reports for long running commands (such as ALTER TABLE). (Defaults to on; use --skip-progress-reports to disable.)
Set the prompt to the specified format. 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.
• --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 escaping.
The following example demonstrates tabular versus nontabular output and the use of raw mode to disable escaping:
If the connection to the server is lost, automatically try to reconnect. A single reconnect attempt is made each time the connection is lost. Enabled by default, to disable use --skip-reconnect or --disable-reconnect.
• --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 format.
Set automatic limit for SELECT when using --safe-updates. (Default value is 1,000.)
Send name as a parameter to the embedded server.
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.
Disable automatic rehashing. Synonym for --disable-auto-rehash.
• --skip-column-names, -N
Do not write column names in results.
• --skip-line-numbers, -L
Do not write line numbers for errors. Useful when you want to compare result files that include error messages.
• --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. Forces --protocol=socket when specified on the command line without other connection properties; on Windows, forces --protocol=pipe.
Enable SSL for connection (automatically enabled with other flags). Disable with --skip-ssl.
CA file in PEM format (check OpenSSL docs, implies --ssl).
CA directory (check OpenSSL docs, implies --ssl).
X509 cert in PEM format (check OpenSSL docs, implies --ssl).
SSL cipher to use (check OpenSSL docs, implies --ssl).
X509 key in PEM format (check OpenSSL docs, implies --ssl).
Certificate revocation list (check OpenSSL docs, implies --ssl).
Certificate revocation list path (check OpenSSL docs, implies --ssl).
Verify server’s "Common Name" in its cert against hostname used when connecting. This option is disabled by default.
• --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 MariaDB 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 mode.)
• --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 aborting.
• --xml, -X
Produce XML output. The output when --xml is used with mysql matches that of mysqldump --xml. See mysqldump(1) for details.
The XML output also uses an XML namespace, as shown here:
mysql --xml -uroot -e "SHOW VARIABLES LIKE
<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 number of seconds before connection timeout. (Default value is 0.)
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 is 16KB.)
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.
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:
• 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 not supported.
• 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. 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.
• 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 used.
• 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 MariaDB. 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, and for parsing the body of stored procedures and functions, triggers, and events.
• 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 tee.
• 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 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.
• 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 logging.
• 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 file:
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 necessary:
mysql> pager less -n -i -S -F -X
• You can specify very complex pager commands for handling query output:
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 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:
• 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:
mysql --prompt="(\u@\h) [\d]> "
• Use an option file. You can set the prompt option in the [mysql] group of any MariaDB 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 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:
prompt (\u@\h) [\d]>\_
PROMPT set to ´(\u@\h) [\d]>\_´
(user@host) [database]> prompt
Returning to default PROMPT of mysql>
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. The proper operation of this command requires that the help tables in the mysql database be initialized with help topic information.
If there is no match for the search string, the search fails:
Please try to run ´help contents´ for a list of all accessible topics
Use help contents to see a list of the help categories:
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 matching topics:
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:
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 |
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> \. 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.
mysql ignores Unicode byte order mark (BOM) characters at the beginning of input files. 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.
This section describes some techniques that can help you use mysql more effectively.
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:
SELECT * FROM mails WHERE LENGTH(txt) < 300 LIMIT
*************************** 1. row ***************************
date: 2000-03-01 23:29:50
reply: monty [AT] no.com
mail_to: "Thimble Smith" <tim [AT] no.com>
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)
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 MariaDB server:
SET sql_safe_updates=1, sql_select_limit=1000, sql_max_join_size=1000000;
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:
tbl_name SET not_key_column=val WHERE
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
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:
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.
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