DECLAREcondition_nameCONDITION FORcondition_valuecondition_value: {mysql_error_code| SQLSTATE [VALUE]sqlstate_value}
The DECLARE ... CONDITION statement declares a named error condition, associating a name with a condition that needs specific handling. DECLARE ... CONDITION语句声明一个命名错误条件，将名称与需要特定处理的条件相关联。The name can be referred to in a subsequent 名称可以在随后的DECLARE ... HANDLER statement (see Section 13.6.7.2, “DECLARE ... HANDLER Statement”).DECLARE ... HANDLER语句中引用（请参阅第13.6.7.2节，“DECLARE ... HANDLER语句”）。
Condition declarations must appear before cursor or handler declarations.条件声明必须出现在游标或处理程序声明之前。
The condition_value for DECLARE ... CONDITION indicates the specific condition or class of conditions to associate with the condition name. DECLARE ... CONDITION的condition_value指示要与条件名称关联的特定条件或条件类别。It can take the following forms:它可以采取以下形式：
mysql_error_code: An integer literal indicating a MySQL error code.表示MySQL错误代码的整数文本。
Do not use MySQL error code 0 because that indicates success rather than an error condition. 不要使用MySQL错误代码0，因为这表示成功，而不是错误条件。For a list of MySQL error codes, see Server Error Message Reference.有关MySQL错误代码的列表，请参阅服务器错误消息参考。
SQLSTATE [VALUE] sqlstate_value: A 5-character string literal indicating an SQLSTATE value.表示SQLSTATE值的5个字符的字符串文字。
Do not use SQLSTATE values that begin with 不要使用以'00' because those indicate success rather than an error condition. '00'开头的SQLSTATE值，因为这些值表示成功，而不是错误条件。For a list of SQLSTATE values, see Server Error Message Reference.有关SQLSTATE值的列表，请参阅服务器错误消息参考。
Condition names referred to in SIGNAL or use RESIGNAL statements must be associated with SQLSTATE values, not MySQL error codes.SIGNAL或使用RESIGNAL语句中引用的条件名称必须与SQLSTATE值关联，而不是与MySQL错误代码关联。
Using names for conditions can help make stored program code clearer. 使用条件名称有助于使存储程序代码更清晰。For example, this handler applies to attempts to drop a nonexistent table, but that is apparent only if you know that 1051 is the MySQL error code for “unknown table”:例如，此处理程序适用于删除不存在的表的尝试，但只有当您知道1051是“unknown table”的MySQL错误代码时，这才是明显的：
DECLARE CONTINUE HANDLER FOR 1051
BEGIN
-- body of handler
END;
By declaring a name for the condition, the purpose of the handler is more readily seen:通过为条件声明名称，可以更容易地看到处理程序的用途：
DECLARE no_such_table CONDITION FOR 1051;
DECLARE CONTINUE HANDLER FOR no_such_table
BEGIN
-- body of handler
END;
Here is a named condition for the same condition, but based on the corresponding SQLSTATE value rather than the MySQL error code:以下是相同条件的命名条件，但基于相应的SQLSTATE值，而不是MySQL错误代码：
DECLARE no_such_table CONDITION FOR SQLSTATE '42S02';
DECLARE CONTINUE HANDLER FOR no_such_table
BEGIN
-- body of handler
END;