126.96.36.199 mysql Client Tips
mysql supports input-line editing, which enables you to modify the current input line in place or recall previous input lines. For example, the left-arrow and right-arrow keys move horizontally within the current input line, and the up-arrow and down-arrow keys move up and down through the set of previously entered lines. Backspace deletes the character before the cursor and typing new characters enters them at the cursor position. To enter the line, press Enter.
On Windows, the editing key sequences are the same as supported for command editing in console windows. On Unix, the key sequences depend on the input library used to build mysql (for example, the
Documentation for the
readline libraries is available online. To change the set of key sequences permitted by a given input library, define key bindings in the library startup file. This is a file in your home directory:
For example, in
libedit, Control+W deletes everything before the current cursor position and Control+U deletes the entire line. In
readline, Control+W deletes the word before the cursor and Control+U deletes everything before the current cursor position. If mysql was built using
libedit, a user who prefers the
readline behavior for these two keys can put the following lines in the
.editrc file (creating the file if necessary):
bind "^W" ed-delete-prev-word bind "^U" vi-kill-line-prev
To see the current set of key bindings, temporarily put a line that says only
bind at the end of
.editrc. mysql will show the bindings when it starts.
The up-arrow key enables you to recall input lines from current and previous sessions. In cases where a console is shared, this behavior may be unsuitable. mysql supports disabling the interactive history partially or fully, depending on the host platform.
On Windows, the history is stored in memory. Alt+F7 deletes all input lines stored in memory for the current history buffer. It also deletes the list of sequential numbers in front of the input lines displayed with F7 and recalled (by number) with F9. New input lines entered after you press Alt+F7 repopulate the current history buffer. Clearing the buffer does not prevent logging to the Windows Event Viewer, if the
--syslog option was used to start mysql. Closing the console window also clears the current history buffer.
To disable interactive history on Unix, first delete the
.mysql_history file, if it exists (previous entries are recalled otherwise). Then start mysql with the
--histignore="*" option to ignore all new input lines. To re-enable the recall (and logging) behavior, restart mysql without the option.
If you prevent the
.mysql_history file from being created (see Controlling the History File) and use
--histignore="*" to start the mysql client, the interactive history recall facility is disabled fully. Alternatively, if you omit the
--histignore option, you can recall the input lines entered during the current session.
Windows provides APIs based on UTF-16LE for reading from and writing to the console; the mysql client for Windows is able to use these APIs. The Windows installer creates an item in the MySQL menu named
MySQL command line client - Unicode. This item invokes the mysql client with properties set to communicate through the console to the MySQL server using Unicode.
To take advantage of this support manually, run mysql within a console that uses a compatible Unicode font and set the default character set to a Unicode character set that is supported for communication with the server:
Open a console window.
Go to the console window properties, select the font tab, and choose Lucida Console or some other compatible Unicode font. This is necessary because console windows start by default using a DOS raster font that is inadequate for Unicode.
Execute mysql.exe with the
utf8mb4) option. This option is necessary because
utf16leis one of the character sets that cannot be used as the client character set. See Impermissible Client Character Sets.
With those changes, mysql will use the Windows APIs to communicate with the console using UTF-16LE, and communicate with the server using UTF-8. (The menu item mentioned previously sets the font and character set as just described.)
To avoid those steps each time you run mysql, you can create a shortcut that invokes mysql.exe. The shortcut should set the console font to Lucida Console or some other compatible Unicode font, and pass the
utf8mb4) option to mysql.exe.
Alternatively, create a shortcut that only sets the console font, and set the character set in the
[mysql] group of your
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: Jones reply: [email protected] mail_to: "John Smith" <[email protected]> sbj: UTF-8 txt: >>>>> "John" == John Smith writes: John> Hi. I think this is a good idea. Is anyone familiar John> with UTF-8 or Unicode? Otherwise, I'll put this on my John> TODO list and see what happens. Yes, please do that. Regards, Jones file: inbox-jani-1 hash: 190402944 1 row in set (0.09 sec)
For beginners, a useful startup option is
--i-am-a-dummy, which has the same effect). Safe-updates mode is helpful for cases when you might have issued an
DELETE statement but forgotten the
WHERE clause indicating which rows to modify. Normally, such statements update or delete all rows in the table. With
--safe-updates, you can modify rows only by specifying the key values that identify them, or a
LIMIT clause, or both. This helps prevent accidents. Safe-updates mode also restricts
SELECT statements that produce (or are estimated to produce) very large result sets.
--safe-updates option causes mysql to execute the following statement when it connects to the MySQL server, to set the session values of the
max_join_size system variables:
SET sql_safe_updates=1, sql_select_limit=1000, max_join_size=1000000;
SET statement affects statement processing as follows:
UPDATE tbl_name SET not_key_column=val WHERE key_column=val; UPDATE tbl_name SET not_key_column=val LIMIT 1;
mysql --safe-updates --select-limit=500 --max-join-size=10000
It is possible for
DELETE statements to produce an error in safe-updates mode even with a key specified in the
WHERE clause, if the optimizer decides not to use the index on the key column:
Range access on the index cannot be used if memory usage exceeds that permitted by the
range_optimizer_max_mem_sizesystem variable. The optimizer then falls back to a table scan. See Limiting Memory Use for Range Optimization.
If key comparisons require type conversion, the index may not be used (see Section 8.3.1, “How MySQL Uses Indexes”). Suppose that an indexed string column
c1is compared to a numeric value using
WHERE c1 = 2222. For such comparisons, the string value is converted to a number and the operands are compared numerically (see Section 12.2, “Type Conversion in Expression Evaluation”), preventing use of the index. If safe-updates mode is enabled, an error occurs.
As of MySQL 5.7.25, safe-updates mode also includes these behaviors:
DELETEstatements does not produce safe-updates errors. This enables use of
SHOW WARNINGSto see why an index is not used, which can be helpful in cases such as when a
range_optimizer_max_mem_sizeviolation or type conversion occurs and the optimizer does not use an index even though a key column was specified in the
When a safe-updates error occurs, the error message includes the first diagnostic that was produced, to provide information about the reason for failure. For example, the message may indicate that the
range_optimizer_max_mem_sizevalue was exceeded or type conversion occurred, either of which can preclude use of an index.
For multiple-table deletes and updates, an error is produced with safe updates enabled only if any target table uses a table scan.
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)
@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
For more information about auto-reconnect and its effect on state information when a reconnection occurs, see Section 27.7.19, “C API Automatic Reconnection Control”.
The mysql client uses a parser on the client side that is not a duplicate of the complete parser used by the mysqld server on the server side. This can lead to differences in treatment of certain constructs. Examples:
The server parser treats strings delimited by
"characters as identifiers rather than as plain strings if the
ANSI_QUOTESSQL mode is enabled.
If it is desirable for mysql not to interpret short-form commands within comments, a partial workaround is to use the
--binary-modeoption, which causes all mysql commands to be disabled except
\din noninteractive mode (for input piped to mysql or loaded using the