13.5. Database Administration Statements

SHOW [GLOBAL | SESSION] STATUS [LIKE 'pattern']

SHOW STATUS provides server status information. This information also can be obtained using the mysqladmin extended-status command.

Partial output is shown here. The list of names and values may be different for your server. The meaning of each variable is given in Section 5.2.4, “Server Status Variables”.

mysql> SHOW STATUS;
+--------------------------+------------+
| Variable_name            | Value      |
+--------------------------+------------+
| Aborted_clients          | 0          |
| Aborted_connects         | 0          |
| Bytes_received           | 155372598  |
| Bytes_sent               | 1176560426 |
| Connections              | 30023      |
| Created_tmp_disk_tables  | 0          |
| Created_tmp_tables       | 8340       |
| Created_tmp_files        | 60         |
...
| Open_tables              | 1          |
| Open_files               | 2          |
| Open_streams             | 0          |
| Opened_tables            | 44600      |
| Questions                | 2026873    |
...
| Table_locks_immediate    | 1920382    |
| Table_locks_waited       | 0          |
| Threads_cached           | 0          |
| Threads_created          | 30022      |
| Threads_connected        | 1          |
| Threads_running          | 1          |
| Uptime                   | 80380      |
+--------------------------+------------+

With a LIKE clause, the statement displays only rows for those variables with names that match the pattern:

mysql> SHOW STATUS LIKE 'Key%';
+--------------------+----------+
| Variable_name      | Value    |
+--------------------+----------+
| Key_blocks_used    | 14955    |
| Key_read_requests  | 96854827 |
| Key_reads          | 162040   |
| Key_write_requests | 7589728  |
| Key_writes         | 3813196  |
+--------------------+----------+

The GLOBAL and SESSION options are new in MySQL 5.0.2. With the GLOBAL modifier, SHOW STATUS displays the status values for all connections to MySQL. With SESSION, it displays the status values for the current connection. If no modifier is present, the default is SESSION. LOCAL is a synonym for SESSION.

Some status variables have only a global value. For these, you get the same value for both GLOBAL and SESSION.

Note: Before MySQL 5.0.2, SHOW STATUS returned global status values. Because the default as of 5.0.2 is to return session values, this is incompatible with previous versions. To issue a SHOW STATUS statement that will retrieve global status values for all versions of MySQL, write it like this:

SHOW /*!50002 GLOBAL */ STATUS;

SHOW TABLE STATUS [FROM db_name] [LIKE 'pattern']

SHOW TABLE STATUS works likes SHOW TABLE, but provides a lot of information about each table. You can also get this list using the mysqlshow --status db_name command.

As of MySQL 5.0.1, this statement also displays information about views.

SHOW TABLE STATUS returns the following fields:

In the table comment, InnoDB tables report the free space of the tablespace to which the table belongs. For a table located in the shared tablespace, this is the free space of the shared tablespace. If you are using multiple tablespaces and the table has its own tablespace, the free space is for only that table.

For MEMORY tables, the Data_length, Max_data_length, and Index_length values approximate the actual amount of allocated memory. The allocation algorithm reserves memory in large amounts to reduce the number of allocation operations.

Beginning with MySQL 5.0.3, for NDB Cluster tables, the output of this statement shows appropriate values for the Avg_row_length and Data_length columns, with the exception that BLOB columns are not taken into account. In addition, the number of replicas is now shown in the Comment column (as number_of_replicas).

For views, all the fields displayed by SHOW TABLE STATUS are NULL except that Name indicates the view name and Comment says view.

SHOW [FULL] TABLES [FROM db_name] [LIKE 'pattern']

SHOW TABLES lists the non-TEMPORARY tables in a given database. You can also get this list using the mysqlshow db_name command.

Before MySQL 5.0.1, the output from SHOW TABLES contains a single column of table names. Beginning with MySQL 5.0.1, this statement also lists any views in the database. As of MySQL 5.0.2, the FULL modifier is supported such that SHOW FULL TABLES displays a second output column. Values for the second column are BASE TABLE for a table and VIEW for a view.

Note: If you have no privileges for a table, the table does not show up in the output from SHOW TABLES or mysqlshow db_name.

SHOW TRIGGERS [FROM db_name] [LIKE expr]

SHOW TRIGGERS lists the triggers currently defined on the MySQL server. This statement requires the SUPER privilege. It was implemented in MySQL 5.0.10.

For the trigger ins_sum as defined in Section 18.3, “Using Triggers”, the output of this statement is as shown here:

mysql> SHOW TRIGGERS LIKE 'acc%'\G
*************************** 1. row ***************************
  Trigger: ins_sum
    Event: INSERT
    Table: account
Statement: SET @sum = @sum + NEW.amount
   Timing: BEFORE
  Created: NULL
 sql_mode:
  Definer: myname@localhost

Note: When using a LIKE clause with SHOW TRIGGERS, the expression to be matched (expr) is compared with the name of the table on which the trigger is declared, and not with the name of the trigger:

mysql> SHOW TRIGGERS LIKE 'ins%';
Empty set (0.01 sec)

A brief explanation of the columns in the output of this statement is shown here:

You must have the SUPER privilege to execute SHOW TRIGGERS.

See also Section 20.16, “The INFORMATION_SCHEMA TRIGGERS Table”.

SHOW [GLOBAL | SESSION] VARIABLES [LIKE 'pattern']

SHOW VARIABLES shows the values of MySQL system variables. This information also can be obtained using the mysqladmin variables command.

With the GLOBAL modifier, SHOW VARIABLES displays the values that are used for new connections to MySQL. With SESSION, it displays the values that are in effect for the current connection. If no modifier is present, the default is SESSION. LOCAL is a synonym for SESSION.

If the default system variable values are unsuitable, you can set them using command options when mysqld starts, and most can be changed at runtime with the SET statement. See Section 5.2.3, “Using System Variables”, and Section 13.5.3, “SET Syntax”.

Partial output is shown here. The list of names and values may be different for your server. Section 5.2.2, “Server System Variables”, describes the meaning of each variable, and Section 7.5.2, “Tuning Server Parameters”, provides information about tuning them.

mysql> SHOW VARIABLES;
+---------------------------------+-------------------------------------+
| Variable_name                   | Value                               |
+---------------------------------+-------------------------------------+
| auto_increment_increment        | 1                                   |
| auto_increment_offset           | 1                                   |
| automatic_sp_privileges         | ON                                  |
| back_log                        | 50                                  |
| basedir                         | /                                   |
| bdb_cache_size                  | 8388600                             |
| bdb_home                        | /var/lib/mysql/                     |
| bdb_log_buffer_size             | 32768                               |
...
| max_connections                 | 100                                 |
| max_connect_errors              | 10                                  |
| max_delayed_threads             | 20                                  |
| max_error_count                 | 64                                  |
| max_heap_table_size             | 16777216                            |
| max_join_size                   | 4294967295                          |
| max_relay_log_size              | 0                                   |
| max_sort_length                 | 1024                                |
...
| time_zone                       | SYSTEM                              |
| timed_mutexes                   | OFF                                 |
| tmp_table_size                  | 33554432                            |
| tmpdir                          |                                     |
| transaction_alloc_block_size    | 8192                                |
| transaction_prealloc_size       | 4096                                |
| tx_isolation                    | REPEATABLE-READ                     |
| updatable_views_with_limit      | YES                                 |
| version                         | 5.0.19-Max                          |
| version_comment                 | MySQL Community Edition - Max (GPL) |
| version_compile_machine         | i686                                |
| version_compile_os              | pc-linux-gnu                        |
| wait_timeout                    | 28800                               |
+---------------------------------+-------------------------------------+

With a LIKE clause, the statement displays only rows for those variables with names that match the pattern. To obtain the row for a specific variable, use a LIKE clause as shown:

SHOW VARIABLES LIKE 'max_join_size';
SHOW SESSION VARIABLES LIKE 'max_join_size';

To get a list of variables whose name match a pattern, use the ‘%’ wildcard character in a LIKE clause:

SHOW VARIABLES LIKE '%size%';
SHOW GLOBAL VARIABLES LIKE '%size%';

Wildcard characters can be used in any position within the pattern to be matched. Strictly speaking, because ‘_’ is a wildcard that matches any single character, you should escape it as ‘\_’ to match it literally. In practice, this is rarely necessary.

SHOW WARNINGS [LIMIT [offset,] row_count]
SHOW COUNT(*) WARNINGS

SHOW WARNINGS shows the error, warning, and note messages that resulted from the last statement that generated messages, or nothing if the last statement that used a table generated no messages. A related statement, SHOW ERRORS, shows only the errors. See Section 13.5.4.11, “SHOW ERRORS Syntax”.

The list of messages is reset for each new statement that uses a table.

The SHOW COUNT(*) WARNINGS statement displays the total number of errors, warnings, and notes. You can also retrieve this number from the warning_count variable:

SHOW COUNT(*) WARNINGS;
SELECT @@warning_count;

The value of warning_count might be greater than the number of messages displayed by SHOW WARNINGS if the max_error_count system variable is set so low that not all messages are stored. An example shown later in this section demonstrates how this can happen.

The LIMIT clause has the same syntax as for the SELECT statement. See Section 13.2.7, “SELECT Syntax”.

The MySQL server sends back the total number of errors, warnings, and notes resulting from the last statement. If you are using the C API, this value can be obtained by calling mysql_warning_count(). See Section 22.2.3.71, “mysql_warning_count()”.

Warnings are generated for statements such as LOAD DATA INFILE and DML statements such as INSERT, UPDATE, CREATE TABLE, and ALTER TABLE.

The following DROP TABLE statement results in a note:

mysql> DROP TABLE IF EXISTS no_such_table;
mysql> SHOW WARNINGS;
+-------+------+-------------------------------+
| Level | Code | Message                       |
+-------+------+-------------------------------+
| Note  | 1051 | Unknown table 'no_such_table' |
+-------+------+-------------------------------+

Here is a simple example that shows a syntax warning for CREATE TABLE and conversion warnings for INSERT:

mysql> CREATE TABLE t1 (a TINYINT NOT NULL, b CHAR(4)) TYPE=MyISAM;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
  Level: Warning
   Code: 1287
Message: 'TYPE=storage_engine' is deprecated, use
         'ENGINE=storage_engine' instead
1 row in set (0.00 sec)

mysql> INSERT INTO t1 VALUES(10,'mysql'),(NULL,'test'),
    -> (300,'Open Source');
Query OK, 3 rows affected, 4 warnings (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 4

mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
  Level: Warning
   Code: 1265
Message: Data truncated for column 'b' at row 1
*************************** 2. row ***************************
  Level: Warning
   Code: 1263
Message: Data truncated, NULL supplied to NOT NULL column 'a' at row 2
*************************** 3. row ***************************
  Level: Warning
   Code: 1264
Message: Data truncated, out of range for column 'a' at row 3
*************************** 4. row ***************************
  Level: Warning
   Code: 1265
Message: Data truncated for column 'b' at row 3
4 rows in set (0.00 sec)

The maximum number of error, warning, and note messages to store is controlled by the max_error_count system variable. By default, its value is 64. To change the number of messages you want stored, change the value of max_error_count. In the following example, the ALTER TABLE statement produces three warning messages, but only one is stored because max_error_count has been set to 1:

mysql> SHOW VARIABLES LIKE 'max_error_count';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_error_count | 64    |
+-----------------+-------+
1 row in set (0.00 sec)

mysql> SET max_error_count=1;
Query OK, 0 rows affected (0.00 sec)

mysql> ALTER TABLE t1 MODIFY b CHAR;
Query OK, 3 rows affected, 3 warnings (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 3

mysql> SELECT @@warning_count;
+-----------------+
| @@warning_count |
+-----------------+
|               3 |
+-----------------+
1 row in set (0.01 sec)

mysql> SHOW WARNINGS;
+---------+------+----------------------------------------+
| Level   | Code | Message                                |
+---------+------+----------------------------------------+
| Warning | 1263 | Data truncated for column 'b' at row 1 |
+---------+------+----------------------------------------+
1 row in set (0.00 sec)

To disable warnings, set max_error_count to 0. In this case, warning_count still indicates how many warnings have occurred, but none of the messages are stored.

As of MySQL 5.0.3, you can set the SQL_NOTES session variable to 0 to cause Note-level warnings not to be recorded.