The diagnostics area contains two kinds of information:诊断区域包含两种信息：

For a statement that produces three conditions, the diagnostics area contains statement and condition information like this:对于产生三个条件的语句，诊断区域包含如下语句和条件信息：

Statement information:
  row count
  ... other statement information items ...
Condition area list:
  Condition area 1:
    error code for condition 1
    error message for condition 1
    ... other condition information items ...
  Condition area 2:
    error code for condition 2:
    error message for condition 2
    ... other condition information items ...
  Condition area 3:
    error code for condition 3
    error message for condition 3
    ... other condition information items ...

The diagnostics area contains statement and condition information items. 诊断区域包含语句和条件信息项。Numeric items are integers. The character set for character items is UTF-8. 数字项是整数。字符项的字符集是UTF-8。No item can be NULL. 任何项都不能为NULL。If a statement or condition item is not set by a statement that populates the diagnostics area, its value is 0 or the empty string, depending on the item data type.如果语句或条件项不是由填充诊断区域的语句设置的，则其值为0或空字符串，具体取决于项数据类型。

The statement information part of the diagnostics area contains these items:诊断区域的语句信息部分包含以下项目：

The condition information part of the diagnostics area contains a condition area for each condition. 诊断区域的条件信息部分包含每个条件的条件区域。Condition areas are numbered from 1 to the value of the NUMBER statement condition item. 条件区域的编号范围从1到NUMBER语句条件项的值。If NUMBER is 0, there are no condition areas.如果NUMBER为0，则不存在条件区域。

Each condition area contains the items in the following list. 每个条件区域包含以下列表中的项目。All items are standard SQL except MYSQL_ERRNO, which is a MySQL extension. 除MYSQL_ERRNO是MYSQL的扩展外，所有项目都是标准SQL。The definitions apply for conditions generated other than by a signal (that is, by a SIGNAL or RESIGNAL statement). 这些定义适用于由信号（即，由SIGNAL或RESIGNAL语句）以外的其他方式生成的条件。For nonsignal conditions, MySQL populates only those condition items not described as always empty. 对于非信号条件，MySQL只填充那些没有被描述为总是空的条件项。The effects of signals on the condition area are described later.信号对条件区域的影响将在后面描述。

For the RETURNED_SQLSTATE, MESSAGE_TEXT, and MYSQL_ERRNO values for particular errors, see Server Error Message Reference.有关返回的特定RETURNED_SQLSTATE、MESSAGE_TEXT和MYSQL_ERRNO值，请参阅服务器错误消息参考。

If a SIGNAL (or RESIGNAL) statement populates the diagnostics area, its SET clause can assign to any condition information item except RETURNED_SQLSTATE any value that is legal for the item data type. 如果SIGNAL（或RESIGNAL）语句填充了诊断区域，则其SET子句可以为任何条件信息项赋值，但RETURNED_SQLSTATE除外，该项数据类型的任何合法值。SIGNAL also sets the RETURNED_SQLSTATE value, but not directly in its SET clause. SIGNAL还设置RETURNED_SQLSTATE值，但不直接在其SET子句中设置。That value comes from the SIGNAL statement SQLSTATE argument.该值来自SIGNAL语句SQLSTATE参数。

SIGNAL also sets statement information items. SIGNAL还设置语句信息项。It sets NUMBER to 1. 它将NUMBER设置为1。It sets ROW_COUNT to −1 for errors and 0 otherwise.它将错误的ROW_COUNT设置为1，否则设置为0。

Nondiagnostic SQL statements populate the diagnostics area automatically, and its contents can be set explicitly with the SIGNAL and RESIGNAL statements. 非诊断SQL语句自动填充诊断区域，其内容可以通过SIGNAL和RESIGNAL语句显式设置。The diagnostics area can be examined with GET DIAGNOSTICS to extract specific items, or with SHOW WARNINGS or SHOW ERRORS to see conditions or errors.可以使用GET DIAGNOSTICS（获取诊断）来检查诊断区域以提取特定项目，或者使用SHOW WARNINGS（显示警告）或SHOW ERRORS（显示错误）来查看条件或错误。

SQL statements clear and set the diagnostics area as follows:SQL语句清除并设置诊断区域，如下所示：

Thus, even a statement that does not normally clear the diagnostics area when it begins executing clears it if the statement raises a condition.因此，即使是在开始执行时通常不清除诊断区域的语句，如果该语句引发条件，也会将其清除。

The following example shows the effect of various statements on the diagnostics area, using SHOW WARNINGS to display information about conditions stored there.以下示例显示了diagnostics（诊断）区域中各种语句的效果，使用SHOW WARNINGS（显示警告）来显示有关存储在该区域的条件的信息。

This DROP TABLE statement clears the diagnostics area and populates it when the condition occurs:此DROP TABLE语句清除诊断区域，并在出现以下情况时填充：

mysql> DROP TABLE IF EXISTS test.no_such_table;
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> SHOW WARNINGS;
+-------+------+------------------------------------+
| Level | Code | Message                            |
+-------+------+------------------------------------+
| Note  | 1051 | Unknown table 'test.no_such_table' |
+-------+------+------------------------------------+
1 row in set (0.00 sec)

This SET statement generates an error, so it clears and populates the diagnostics area:此SET语句生成错误，因此会清除并填充诊断区域：

mysql> SET @x = @@x;
ERROR 1193 (HY000): Unknown system variable 'x'

mysql> SHOW WARNINGS;
+-------+------+-----------------------------+
| Level | Code | Message                     |
+-------+------+-----------------------------+
| Error | 1193 | Unknown system variable 'x' |
+-------+------+-----------------------------+
1 row in set (0.00 sec)

The previous SET statement produced a single condition, so 1 is the only valid condition number for GET DIAGNOSTICS at this point. 上一个SET语句生成了一个条件，因此1是此时GET DIAGNOSTICS的唯一有效条件号。The following statement uses a condition number of 2, which produces a warning that is added to the diagnostics area without clearing it:以下语句使用的条件编号为2，会产生一个警告，该警告会添加到诊断区域，而不会清除该区域：

mysql> GET DIAGNOSTICS CONDITION 2 @p = MESSAGE_TEXT;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> SHOW WARNINGS;
+-------+------+------------------------------+
| Level | Code | Message                      |
+-------+------+------------------------------+
| Error | 1193 | Unknown system variable 'xx' |
| Error | 1753 | Invalid condition number     |
+-------+------+------------------------------+
2 rows in set (0.00 sec)

Now there are two conditions in the diagnostics area, so the same GET DIAGNOSTICS statement succeeds:现在diagnostics区域中有两种情况，因此相同的GET DIAGNOSTICS语句会成功：

mysql> GET DIAGNOSTICS CONDITION 2 @p = MESSAGE_TEXT;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @p;
+--------------------------+
| @p                       |
+--------------------------+
| Invalid condition number |
+--------------------------+
1 row in set (0.01 sec)

When a push to the diagnostics area stack occurs, the first (current) diagnostics area becomes the second (stacked) diagnostics area and a new current diagnostics area is created as a copy of it. 当推送到诊断区域堆栈时，第一个（当前）诊断区域成为第二个（堆叠）诊断区域，并创建一个新的当前诊断区域作为其副本。Diagnostics areas are pushed to and popped from the stack under the following circumstances:在以下情况下，诊断区域被推送到堆栈中并从堆栈中弹出：

Certain system variables control or are related to some aspects of the diagnostics area:某些系统变量控制或与诊断领域的某些方面有关：

Example: If max_error_count is 10, the diagnostics area can contain a maximum of 10 condition areas. 示例：如果max_error_count为10，则诊断区域最多可包含10个条件区域。Suppose that a statement raises 20 conditions, 12 of which are errors. 假设一条语句引发20个条件，其中12个是错误。In that case, the diagnostics area contains the first 10 conditions, NUMBER is 10, warning_count is 20, and error_count is 12.在这种情况下，诊断区域包含前10个条件，NUMBER为10，warning_count为20，error_count为12。

Changes to the value of max_error_count have no effect until the next attempt to modify the diagnostics area. 在下次尝试修改诊断区域之前，对max_error_count值的更改无效。If the diagnostics area contains 10 condition areas and max_error_count is set to 5, that has no immediate effect on the size or content of the diagnostics area.如果诊断区域包含10个条件区域，且max_error_count设置为5，则不会立即影响诊断区域的大小或内容。