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. It shows nothing if the last statement used a table and generated no messages. (That is, a statement that uses a table but generates no messages clears the message list.) Statements that do not use tables and do not generate messages have no effect on the message list.

SHOW WARNINGS is implemented as of MySQL 4.1.0. A related statement, SHOW ERRORS, shows only the errors. See Section 12.5.4.9, “SHOW ERRORS Syntax”.

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 12.2.7, “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 17.2.3.70, “mysql_warning_count()”.

Note that the framework for warnings was added in MySQL 4.1.0, at which point many statements did not generate warnings. In 4.1.1, the situation is much improved, with warnings 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 4.1.11, you can set the SQL_NOTES session variable to 0 to cause Note-level warnings not to be recorded.