带你轻松接触MySQL数据库的异常处理

对于MySQL的异常处理，本人不常用。不过我觉得还是有写下来的必要。
标准格式
DECLARE handler_type HANDLER FOR condition_value[,...] statement

handler_type:
CONTINUE
| EXIT
| UNDO --暂时不支持

condition_value:
SQLSTATE [VALUE] sqlstate_value
| condition_name
| SQLWARNING
| NOT FOUND
| SQLEXCEPTION
| mysql_error_code
condition_value细节
1、MySQL ERROR CODE 列表
如果需要查看更多的错误列表可以直接到MySQL安装路径下。
比如我的/usr/local/mysql/share/mysql/errmsg.txt
说明：SQLSTATE [VALUE] sqlstate_value这种格式是专门为ANSI SQL 和 ODBC以及其他的标准.
并不是所有的MySQL ERROR CODE 都映射到SQLSTATE。
2、假如不需要插入ERROR CODE，可以用速记条件来代替
SQLWARNING 代表所有以01开头的错误代码
NOT FOUND 代表所有以02开头的错误代码，当然也可以代表一个游标到达数据集的末尾。
SQLEXCEPTION 代表除了SQLWARNING和NOT FOUND 的所有错误代码。
3、具体示例：
CREATE TABLE t (s1 int,primary key (s1));
mysql> use t_girl
Database changed
mysql> CREATE TABLE t (s1 int,primary key (s1));
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql>
mysql> DELIMITER ||
mysql> CREATE PROCEDURE handlerdemo ()
-> BEGIN
-> DECLARE EXIT HANDLER FOR SQLSTATE '23000' BEGIN END; -- 遇到重复键值就退出

-> SET @x = 1;
-> INSERT INTO t VALUES (1);
-> SET @x = 2;
-> INSERT INTO t VALUES (1);
-> SET @x = 3;
-> END||
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;
mysql> call handlerdemo();
Query OK, 0 rows affected (0.00 sec)

mysql> select @x;
+------+

| @x |
+------+

| 2 |
+------+

1 row in set (0.00 sec)

mysql> call handlerdemo();
Query OK, 0 rows affected (0.00 sec)

mysql> select @x;
+------+

| @x |
+------+

| 1 |
+------+

1 row in set (0.00 sec)

mysql>


遇到错误继续的情况

mysql> truncate table t;
Query OK, 0 rows affected (0.01 sec)

mysql> DELIMITER $$
mysql> DROP PROCEDURE IF EXISTS `t_girl`.`handlerdemo`$$
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE DEFINER=`root`@`localhost` PROCEDURE `handlerdemo`()
-> BEGIN
-> DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' BEGIN END;
-> SET @x = 1;
-> INSERT INTO t VALUES (1);
-> SET @x = 2;
-> INSERT INTO t VALUES (1);
-> SET @x = 3;
-> END$$
Query OK, 0 rows affected (0.01 sec)

mysql> DELIMITER ;
mysql> call handlerdemo();
Query OK, 0 rows affected (0.00 sec)

mysql> select @x;
+------+

| @x |
+------+

| 3 |
+------+

1 row in set (0.00 sec)

mysql> call handlerdemo();
Query OK, 0 rows affected (0.00 sec)

mysql> select @x;
+------+

| @x |
+------+

| 3 |
+------+

1 row in set (0.00 sec)

mysql>

我们可以看到，始终执行到最后。
当然，上面的SQLSTATE '23000'可以替换为1062。

警告：

mysql> alter table t add s2 int not null;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

这个列没有默认值，插入的时候会出现警告或者1364错误提示。
mysql> DELIMITER $$
mysql> DROP PROCEDURE IF EXISTS `t_girl`.`handlerdemo`$$
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> CREATE DEFINER=`root`@`localhost` PROCEDURE `handlerdemo`()
-> BEGIN
-> DECLARE CONTINUE HANDLER FOR 1062 BEGIN END;
-> DECLARE CONTINUE HANDLER FOR SQLWARNING
-> BEGIN
-> update t set s2 = 2;
-> END;
-> DECLARE CONTINUE HANDLER FOR 1364
-> BEGIN
-> INSERT INTO t(s1,s2) VALUES (1,3);
-> END;
-> SET @x = 1;
-> INSERT INTO t(s1) VALUES (1);
-> SET @x = 2;
-> INSERT INTO t(s1) VALUES (1);
-> SET @x = 3;
-> END$$
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> call handlerdemo();
Query OK, 0 rows affected (0.00 sec)

mysql> select * from t;
+----+----+

| s1 | s2 |
+----+----+

| 1 | 3 |
+----+----+

1 row in set (0.00 sec)
遇到错误时，插入的新记录。

mysql> select @x;
+------+

| @x |
+------+

| 3 |
+------+

1 row in set (0.00 sec)