4.5.7.9 SHOW WARNINGS | ERRORS

SHOW WARNINGS [LIMIT row_count]
SHOW ERRORS [LIMIT row_count]

This command is implemented in MySQL 4.1.0.

It shows the errors, warnings and notes that one got for the last command. The errors/warnings are reset for each new command that uses a table.

The MySQL server sends back the total number of warnings and errors you got for the last commend; This can be retrieved by calling mysql_warning_count().

Up to max_error_count messages are stored (Global and thread specific variable).

You can retrieve the number of errors from @error_count and warnings from @warning_count.

SHOW WARNINGS shows all errors, warnings and notes you got for the last command while SHOW ERRORS only shows you the errors.

mysql> DROP TABLE IF EXISTS no_such_table;
mysql> SHOW WARNINGS;

+-------+------+-------------------------------+
| Level | Code | Message                       |
+-------+------+-------------------------------+
| Note  | 1051 | Unknown table 'no_such_table' |
+-------+------+-------------------------------+

Note that in MySQL 4.1.0 we have just added the frame work for warnings and not many MySQL command do yet generate warnings. 4.1.1 supports all kind of warnings for LOAD DATA INFILE and DML statements such as INSERT, UPDATE and ALTER commands.

For example, here is a simple case which produces conversion warnings for a insert statement.

mysql> create table t1(a tinyint NOT NULL, b char(4));
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1 values(10,'mysql'),(NULL,'test'),(300,'open source');
Query OK, 3 rows affected, 4 warnings (0.15 sec)
Records: 3  Duplicates: 0  Warnings: 4

mysql> show warnings;
+---------+------+---------------------------------------------------------------+
| Level   | Code | Message                                                       |
+---------+------+---------------------------------------------------------------+
| Warning | 1263 | Data truncated for column 'b' at row 1                        |
| Warning | 1261 | Data truncated, NULL supplied to NOT NULL column 'a' at row 2 |
| Warning | 1262 | Data truncated, out of range for column 'a' at row 3          |
| Warning | 1263 | Data truncated for column 'b' at row 3                        |
+---------+------+---------------------------------------------------------------+
4 rows in set (0.00 sec)

Maximum number of warnings can be specified using the server variable 'max_error_count', SET max_error_count=[count]; By default it is 64. In case to disable warnings, simply reset this variable to '0'. In case if max_error_count is 0, then still the warning count represents how many warnings have occurred, but none of the messages are stored.

For example, consider the following ALTER table statement for the above example, which returns only one warning message even though total warnings occurred is 3 when you set max_error_count=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> show warnings;
+---------+------+----------------------------------------+
| Level   | Code | Message                                |
+---------+------+----------------------------------------+
| Warning | 1263 | Data truncated for column 'b' at row 1 |
+---------+------+----------------------------------------+
1 row in set (0.00 sec)

mysql>

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