DECLARE handler_type HANDLER FOR condition_value[,...] statement
handler_type:
  CONTINUE
 | EXIT
 | UNDO --这个暂时不支持
condition_value:
  SQLSTATE [VALUE] sqlstate_value
 | condition_name
 | SQLWARNING
 | NOT FOUND
 | SQLEXCEPTION
 | mysql_error_code
condition_value细节

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> 

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> 

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

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)

mysql> select @x;
+------+
| @x |
+------+
| 3 | 
+------+
1 row in set (0.00 sec)