Error Handling 异常处理
好了,我们现在要讲的是异常处理
1. Sample Problem: Log Of Failures 问题样例:故障记录
当INSERT失败时,我希望能将其记录在日志文件中我们用来展示出错处理的问题样例是很
普通的。我希望得到错误的记录。当INSERT失败时,我想在另一个文件中记下这些错误的信息,例如出错时间,出错原因等。我对插入特别感兴趣的原因是它将违反外键关联的约束
2. Sample Problem: Log Of Failures (2)
mysql> CREATE TABLE t2
s1 INT, PRIMARY KEY (s1))
engine=innodb;//
mysql> CREATE TABLE t3 (s1 INT, KEY (s1),
FOREIGN KEY (s1) REFERENCES t2 (s1))
engine=innodb;//
mysql> INSERT INTO t3 VALUES (5);//
...
ERROR 1216 (23000): Cannot add or update a child row: a foreign key
constraint fails(这里显示的是系统的出错信息)
CREATE TABLE error_log (error_message
CHAR(80))//
下一步就是建立一个在做插入动作出错时存储错误的表。
CREATE PROCEDURE p22 (parameter1 INT)
BEGIN
DECLARE EXIT HANDLER FOR 1216
INSERT INTO error_log VALUES
(CONCAT(‘Time: ‘,current_date,
‘. Foreign Key Reference Failure For
Value = ‘,parameter1));
INSERT INTO t3 VALUES (parameter1);
END;//
CALL p22 (5) //
DECLARE
{ EXIT | CONTINUE }
HANDLER FOR
{ error-number | { SQLSTATE error-string } | condition }
SQL statement
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
CREATE TABLE t4 (s1 int,primary key(s1));//
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;//
mysql> CALL p23()//
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT @x, @x2//
+------+------+
| @x | @x2 |
+------+------+
| 3 | 1 |
+------+------+
1 row in set (0.00 sec)
CREATE PROCEDURE p24 ()
BEGIN
DECLARE `Constraint Violation`
CONDITION FOR SQLSTATE ‘23000‘;
DECLARE EXIT HANDLER FOR
`Constraint Violation` ROLLBACK;
START TRANSACTION;
INSERT INTO t2 VALUES (1);
INSERT INTO t2 VALUES (1);
COMMIT;
END; //
CREATE PROCEDURE p24 ()
BEGIN
DECLARE `Constraint Violation`
CONDITION FOR SQLSTATE ‘23000‘;
DECLARE EXIT HANDLER FOR
`Constraint Violation` ROLLBACK;
START TRANSACTION;
INSERT INTO t2 VALUES (1);
INSERT INTO t2 VALUES (1);
COMMIT;
END; //
mysql> CALL p24()//
Query OK, 0 rows affected (0.28 sec)
mysql> SELECT * FROM t2//
Empty set (0.00 sec)
mysql> CREATE PROCEDURE p9 ()
-> BEGIN
-> DECLARE EXIT HANDLER FOR NOT FOUND BEGIN END;
-> DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN END;
-> DECLARE EXIT HANDLER FOR SQLWARNING BEGIN END;
-> END;//
Query OK, 0 rows affected (0.00 sec)
Cursors 游标
游标实现功能摘要:
DECLARE cursor-name CURSOR FOR SELECT ...;
OPEN cursor-name;
FETCH cursor-name INTO variable [, variable];
CLOSE cursor-name;
现在我们开始着眼游标了。虽然我们的存储过程中的游标语法还并没有完整的实现,但是已经可以完成基本的事务如声明游标,打开游标,从游标里读取,关闭游标。
1. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
我们看一下包含游标的存储过程的新例子。
2. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT; <--
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
这个过程开始声明了三个变量。附带说一下,顺序是十分重要的。首先要进行变量声明,然后声明条件,随后声明游标,再后面才是声明错误处理器。如果你没有按顺序声明,系统会提示错误信息。
3. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t; <--
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
程序第二步声明了游标cur_1,如果你使用过嵌入式SQL的话,就知道这和嵌入式SQL差不多。
4. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND <--
SET b = 1; <--
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
最后进行的是错误处理器的声明。这个CONTINUE处理没有引用SQL错误代码和SQLSTATE值。它使用的是NOT FOUND系统返回值,这和SQLSTATE 02000是一样的。
5. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1; <--
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
过程第一个可执行的语句是OPEN cur_1,它与SELECT s1 FROM t语句是关联的,过程将执行SELECT s1 FROM t,返回一个结果集。
6. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a; <--
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
这里第一个FETCH语句会获得一行从SELECT产生的结果集中检索出来的值,然而表t中有多行,因此这个语句会被执行多次,当然这是因为语句在循环块内。
7. Cursor ExampleCREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1; <--
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
8. Cursor Example
CREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1; <--
SET return_val = a;
END;//
CREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a; <--
END;//
CREATE PROCEDURE p25 (OUT return_val INT)
BEGIN
DECLARE a,b INT;
DECLARE cur_1 CURSOR FOR SELECT s1 FROM t;
DECLARE CONTINUE HANDLER FOR NOT FOUND
SET b = 1;
OPEN cur_1;
REPEAT
FETCH cur_1 INTO a;
UNTIL b = 1
END REPEAT;
CLOSE cur_1;
SET return_val = a;
END;//
mysql> CALL p25(@return_val)//
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT @return_val//
+-------------+
| @return_val |
+-------------+
| 5 |
+-------------+
1 row in set (0.00 sec)
FETCH cursor1 INTO variable1;
UPDATE t1 SET column1 = ‘value1‘ WHERE CURRENT OF cursor1;
FETCH PRIOR cursor1 INTO variable1;
FETCH ABSOLUTE 55 cursor1 INTO variable1;
GRANT CREATE ROUTINE
ON database-name . *
TO user(s)
[WITH GRANT OPTION];
GRANT EXECUTE ON p TO peter
[WITH GRANT OPTION];
GRANT SHOW ROUTINE ON db6.* TO joey
[WITH GRANT OPTION];
CREATE PROCEDURE p26 ()
SQL SECURITY INVOKER
SELECT COUNT(*) FROM t //
CREATE PROCEDURE p27 ()
SQL SECURITY DEFINER
SELECT COUNT(*) FROM t //
GRANT INSERT ON db5.* TO peter; //
/* Logged on with current_user = peter */使用帐户peter登陆
mysql> CALL p26();
ERROR 1142 (42000): select command denied to user
‘peter‘@‘localhost‘ for table ‘t‘
mysql> CALL p27();
+----------+
| COUNT(*) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)
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