声明异常处理的语法
DECLARE
{EXIT | CONTINUE}
HANDLER FOR
{error-number | SQLSTATE error-string | condition}
SQL statement
上述定义包括：
Handler Type （CONTINUE,EXIT）//处理类型 继续或退出
Handler condition （SQLSTATE,MYSQL ERROR,CONDITION）//触发条件
Handler actions（错误触发的操作）
注意：
1、exit只退出当前的block。exit 意思是当动作成功提交后，退出所在的复合语句。即declare exit handler for... 所在的复合语句。
2、如果定义了handler action，会在continue或exit之前执行
发生错误的条件有：
1、MYSQL错误代码
2、ANSI-standard SQLSTATE code
3、命名条件。可使用系统内置的SQLEXCEPTION,SQLWARNING和NOT FOUND
例1：
当错误代码为1062时将duplicate_key的值设为1，并继续执行当前任务
declare continue handler for 1062 set duplicate_key=1;
下面的跟上面一样，只是使用的条件为ANSI标准错误代码
declare continue handler for sqlstate '23000' set duplicate_key=1;
当发生SQLEXCEPTION时，将L_error设为1，并继续
declare continue handler for SQLEXCEPTION set L_error=1;
小提示：
当你在MYSQL客户端执行命令并产生错误时，会得到MYSQL和ANSI的SQLSTATE code，如：
附常见错误号对照表
MySQL error code SQLSTATE code Error message
1011 HY000 Error on delete of '%s' (errno: %d)
1021 HY000 Disk full (%s); waiting for someone to free some space . . .
1022 23000 Can't write; duplicate key in table '%s'
1027 HY000 '%s' is locked against change
1036 HY000 Table '%s' is read only
1048 23000 Column '%s' cannot be null
1062 23000 Duplicate entry '%s' for key %d
1099 HY000 Table '%s' was locked with a READ lock and can't be updated
1100 HY000 Table '%s' was not locked with LOCK TABLES
1104 42000 The SELECT would examine more than MAX_JOIN_SIZE rows; check your WHERE and use SET SQL_BIG_SELECTS=1 or SET SQL_MAX_JOIN_SIZE=# if the SELECT is okay
1106 42000 Incorrect parameters to procedure '%s'
1114 HY000 The table '%s' is full
1150 HY000 Delayed insert thread couldn't get requested lock for table %s
1165 HY000 INSERT DELAYED can't be used with table '%s' because it is locked with LOCK TABLES
1242 21000 Subquery returns more than 1 row
1263 22004 Column set to default value; NULL supplied to NOT NULL column '%s' at row %ld
1264 22003 Out of range value adjusted for column '%s' at row %ld
1265 1000 Data truncated for column '%s' at row %ld
1312 0A000 SELECT in a stored program must have INTO
1317 70100 Query execution was interrupted
1319 42000 Undefined CONDITION: %s
1325 24000 Cursor is already open
1326 24000 Cursor is not open
1328 HY000 Incorrect number of FETCH variables
1329 2000 No data to FETCH
1336 42000 USE is not allowed in a stored program
1337 42000 Variable or condition declaration after cursor or handler declaration
1338 42000 Cursor declaration after handler declaration
1339 20000 Case not found for CASE statement
1348 HY000 Column '%s' is not updatable
1357 HY000 Can't drop a %s from within another stored routine
1358 HY000 GOTO is not allowed in a stored program handler
1362 HY000 Updating of %s row is not allowed in %s trigger
1363 HY000 There is no %s row in %s trigger
命名条件：
declare conditon_name condition for {SQLSTATE sqlstate_code | MYSQL_ERROR_CODE};
例如：
declare foreign_key_error condition for 1216;
declare continue handler for foreign_key_error mysql_statements;
优先级：当同时使用MYSQL错误码，标准SQLSTATE错误码，命名条件（SQLEXCEPTION）来定义错误处理时，其捕获顺序是（只捕获一条错误）：MYSQL码->SQLSTATE->命名条件
作用域：
1、包括begin...end内的语句
declare continue handler for 1048 select 'attempt to insert a null value';
begin
insert into a values(6,null);
end;
若a表第二字段定义为非空，则会触发1048错误
2、若错误处理在begin...end内定义，则在之外的语句不会触发错误发生
BEGIN
BEGIN
DECLARE CONTINUE HANDLER FOR 1216 select 'Foreign key constraint violated';
END;
INSERT INTO departments (department_name,manager_id,location) VALUES ('Elbonian HR','Catbert','Catbertia');
END;
3、能够捕获其它存储过程抛出的错误
下面再通过几个例子来掌握MySQL存储过程中异常处理的使用。
例一：error-number
准备工作
CREATE TABLE `t1` (
`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;
CREATE TABLE `t2` (
`cid` INT(10) UNSIGNED NULL DEFAULT NULL,
INDEX `FK__t1` (`cid`),
CONSTRAINT `FK__t1` FOREIGN KEY (`cid`) REFERENCES `t1` (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;
创建存储过程
delimiter //
create procedure a(var1 int)
begin
declare exit handler for 1452 insert into error_log values(
concat('time:',current_date,'.Foreign Key Reference Failure For Value=',var1)
);
insert into t2 values(var1);
end;//
如果有1452错误，则当插入到表error_log这个语句完成后，退出（exit），这里申明异常处理的语句在上面begin...end的复合语句中，所以这里退出，其实就表示退出了该存储过程。
例二：sqlstate error-string
准备工作
CREATE TABLE `t4` (
`id` INT(10) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`id`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;
create procedure p23()
begin
begin
declare exit handler for sqlstate '23000' set @x2=1;
set @x=1;
insert into t4 values(1);
set @x=2;
end;
begin
declare exit handler for sqlstate '23000' set @x2=9;
insert into t4 values(1);
end;
set @x=3;
end
结果：
例三：
begin
declare exit handler for sqlstate '23000' set @x2=1;
set @x=1;
insert into t4 values(1);
set @x=2;
begin
declare exit handler for sqlstate '23000' set @x2=9;
insert into t4 values(1);
end;
set @x=3;
end
结果：
在执行一次该存储过程，得到结果如下：
error-number的例子
create procedure p22(var1 int)
begin
declare exit handler for 1216 insert into error_log values(
concat('time:' , current_date , '.Foreign Key Reference Failure For Value='
,var1)
);
insert into t3 values(var1);
end;//
sqlstate error-string的例子
create procedure p23()
begin
declare continue handler for sqlstate '23000' set @x2=1;
set @x=1;
insert into t4 values(1);
set @x=2;
insert into t4 values(1);
set @x=3;
end;//
执行结果：
condition的例子
declare 'name' condition for sqlstate '23000';
declare exit handler for 'name' rollback;
