MySQL中的异常处理,游标

一、异常处理的理解
ERROR 1062 (23000): Duplicate entry ‘2’ for key ‘PRIMARY’
错误 4位error code（5位sql statis）：错误内容

二、异常处理的重要性
没有异常处理的存储过程，执行过程中非常难以预测执行结果。
建议：存储过程中加上异常处理部分。

三、异常处理的实现

异常处理的格式：
DECLARECONTINUE/EXITHANDLER FORSQLSTATE ‘23000’ （错误代码）
1.错误是什么？
eg：1062（23000）
2.怎么处理错误？
先执行SQL，再执行EXIT/CONTINUE

小结：
针对什么错误，首先执行SQL语句，可以是一个begin..end;语句块；
根据是continue还是exit，确定是接着执行还是退出begin..end；
接着执行的话，就是接着执行出错的SQL的下一条语句；
如果是退出，就退出这个declare所在的begin…end。

例子1：

DELIMITER $$
CREATE  PROCEDURE small_mistake1(  
  OUT error VARCHAR(5))   
 BEGIN
   DECLARE CONTINUE HANDLER FOR SQLSTATE '23000'   --》这是个异常
     SET error = '23000';      //用来记录错误发生时的一些信息，异常捕获、处理
     select error;
     SET error = '00000';
     select error;
   INSERT INTO TEAMS VALUES(2,27,'third');
   SET error = '23001';      
 END$$
DELIMITER ;

执行结果：

mysql> call small_mistake1(@a);    --》上来直接就是select error，因为先执行sql
+-------+
| error |
+-------+
| NULL  |
+-------+
1 row in set (0.00 sec)
+-------+
| error |
+-------+
| 00000 |
+-------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)

mysql> select @a;    --》
+-------+
| @a    |
+-------+
| 23001 |
+-------+
1 row in set (0.00 sec)

===例子2：

CREATE TABLE test.t (s1 INT, PRIMARY KEY (s1));
delimiter $$
CREATE PROCEDURE handlerdemo ()
BEGIN
  DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1;  
  SET @x = 1;
  INSERT INTO test.t VALUES (1);   ---》能执行
  SET @x = 2;            --》报错，因为@x==1
  INSERT INTO test.t VALUES (1);
  SET @x = 3;
END$$
delimiter ;
CALL handlerdemo()

执行结果：

mysql> select @x2;        --》捕获到异常，就令x2=1
+------+
| @x2  |
+------+
|    1 |
+------+
1 row in set (0.00 sec)
mysql> select @x;        --》set @x=3
+------+
| @x   |
+------+
|    3 |
+------+
1 row in set (0.00 sec)

===例子3：

DELIMITER $$
CREATE  PROCEDURE small_mistake2(  
  OUT error VARCHAR(5))   
 BEGIN
   DECLARE EXIT HANDLER FOR SQLSTATE '23000'      --》EXIT直接退出begin..end
     SET error = '23000';   
     select error;
     SET error = '00000';
     select error;
   INSERT INTO TEAMS VALUES(2,27,'third');  
--》此语句出错，捕获到异常后，因为是exit，所以不会再执行下面的set error='23001'语句
   SET error = '23001';      
 END$$
DELIMITER ;
mysql> call small_mistake2(@a);    --》先执行sql
+-------+
| error |
+-------+
| NULL  |
+-------+
1 row in set (0.00 sec)    --》捕获到异常
+-------+
| error |
+-------+
| 00000 |
+-------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
mysql> select @a;            ---》证明没有执行set error='23001'
+-------+
| @a    |
+-------+
| 23000 |
+-------+
1 row in set (0.00 sec)

===例子4：一个begin后面可以接多个DECLARE

DELIMITER $$
CREATE  PROCEDURE small_mistake3(  
  OUT error VARCHAR(5))   
 BEGIN
   DECLARE CONTINUE HANDLER FOR SQLSTATE '23000'  
     SET error = '23000';   
   DECLARE CONTINUE HANDLER FOR SQLSTATE '21S01'  
     SET error = '21S01';
   INSERT INTO TEAMS VALUES(2,27,'third',5);    
 END$$
DELIMITER ;

mysql> call small_mistake3(@error);
Query OK, 0 rows affected (0.00 sec)
mysql> select @error;
+--------+
| @error |
+--------+
| 21S01  |
+--------+
1 row in set (0.00 sec)

四、错误捕获快捷方式
异常处理的好处：
①出错不报错
②出错可以进行处理；记录出错时的一些信息
③处理所有的错误：
===例子1：

DELIMITER $$
CREATE  PROCEDURE small_mistake5(  
  OUT error VARCHAR(5))   
 BEGIN
   DECLARE CONTINUE HANDLER FOR SQLWARNING,NOT FOUND,SQLEXCEPTION  
---》错误是1开头的赋给SQLWARNING，2开头的NOT FOUND，其他给SQLEXCEPTION
     SET error = 'xxxxx';   
   INSERT INTO teams VALUES(2,27,'third');    
 END$$
DELIMITER ;
mysql> call small_mistake5(@a);
Query OK, 0 rows affected (0.00 sec)
mysql> select @a;
+-------+
| @a    |
+-------+
| xxxxx |
+-------+
1 row in set (0.00 sec)

===忽略一个错误：
忽略一个条件

DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN END; 

–》碰到1开头的就过。

五、异常处理嵌套问题
例子1：增加程序的可读性。

DELIMITER $$
CREATE  PROCEDURE small_mistake6(  
  OUT error VARCHAR(5))   
 BEGIN
   DECLARE non_unique CONDITION FOR SQLSTATE '23000';   
   DECLARE CONTINUE HANDLER FOR non_unique
     begin  
     SET error = '23000';
     select error;
     end;   
     INSERT INTO TEAMS VALUES(2,27,'third');   
 END$$
DELIMITER ;
mysql> call small_mistake6(@error);
+-------+
| error |
+-------+
| 23000 |
+-------+
1 row in set (0.01 sec)

例子2：异常处理的嵌套

DELIMITER $$
CREATE  PROCEDURE small_mistake7()   
 BEGIN     
   DECLARE CONTINUE HANDLER FOR SQLSTATE '23000'  
     SET @processed = 100;   
   BEGIN       
      DECLARE CONTINUE HANDLER FOR SQLSTATE '21000'  
          SET @processed = 200;     
      INSERT INTO TEAMS VALUES(2,27,'third');    
--》出错，假设能被内层的捕获，就执行200；若不能被内层捕获，内层的begin...end就废了，就执行外层100
   END;
 END$$
DELIMITER ;

mysql> call small_mistake7;
Query OK, 0 rows affected (0.00 sec)
mysql> select @processed;
+------------+
| @processed |
+------------+
|        100 |
+------------+
1 row in set (0.00 sec)

====小结
当有多层begin…end的时候，最好每层都有自己完善的异常处理。自己异常，自己这层去处理。

六、游标 CURSOR
游标：处理结果集。多行多列
====例子1：

DELIMITER $$
CREATE  PROCEDURE number_of_players(
  OUT pnumber INTEGER
)   
 BEGIN 
   DECLARE a_playerno INTEGER;    --》变量1
   DECLARE FOUND BOOLEAN DEFAULT TRUE;    --》变量2
   DECLARE c_players CURSOR FOR    --》声明游标（将游标和sql语句关联起来）
     SELECT playerno FROM PLAYERS;
   DECLARE CONTINUE HANDLER FOR NOT FOUND  --》异常处理，所有的以2开头的错误
     SET FOUND = FALSE;     --》异常处理后FOUND变为false
SET pnumber = 0;   
OPEN c_players;    --》打开游标（将游标和结果集联系起来）
   FETCH c_players INTO a_playerno;    --》fetch...into相当于select into
   WHILE FOUND DO
     SET pnumber = pnumber + 1;
     FETCH c_players INTO a_playerno;    --》循环中的fetch...into，依次指向结果集的一个
   END WHILE;    
   CLOSE c_players;
 END$$
DELIMITER ;

mysql> call number_of_players(@pnumber);
Query OK, 0 rows affected (0.00 sec)
mysql> select @pnumber;
+----------+
| @pnumber |
+----------+
|       14 |
+----------+
1 row in set (0.00 sec)

游标处理方式小结：

• 定义游标：将一个游标和一个select进行关联；
• 打开游标：将一个游标和一个结果集关联，执行了select；
• 获取游标（获取结果集）：需要使用循环进行游标的获取。

{注意：当获取到最后一个结果集时，再次执行循环的时候，会报错，这个错误以2开头，
这个时候，需要定义一个对2开头的错误的捕获：

DECLARE CONTINUE HANDLER FOR NOT FOUND 
     SET FOUND = FALSE; }

• 关闭游标：结果集消失
• 资源释放。

七、存储过程权限问题

mysql>select ROUTINE_NAME,ROUTINE_SCHEMA,ROUTINE_TYPE from ROUTINES where ROUTINE_SCHEMA in('test','TENNIS');

GRANT  EXECUTE             --》授予执行权限
   ON PROCEDURE  number_penalties
   TO  'u1'@'%';

[root@mysqlstudy ~]# mysql -uu1 -p12345678
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or g.
Your MySQL connection id is 7
Server version: 5.7.10 MySQL Community Server (GPL)

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

mysql> use TENNIS;
Database changed
mysql> call number_penalties(44,@pnumber);
Query OK, 0 rows affected (0.01 sec)

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