MySQL存储程序之Error Handling

1，简介
MySQL支持HANDLER来处理错误：
Duplicate entry Handler

CREATE PROCEDURE sp_add_location
    (in_location    VARCHAR(30),
     in_address1    VARCHAR(30),
     in_address2    VARCHAR(30),
     zipcode        VARCHAR(10),
     OUT out_status VARCHAR(30))
BEGIN
    DECLARE CONTINUE HANDLER
        FOR 1062
        SET out_status='Duplicate Entry';

    SET out_status='OK';
    INSERT INTO locations
        (location,address1,address2,zipcode)
    VALUES
        (in_location,in_address1,in_address2,zipcode);
END;

Last Row Handler

CREATE PROCEDURE sp_not_found()
    READS SQL DATA
BEGIN
    DECLARE l_last_row INT DEFAULT 0;
    DECLARE l_dept_id INT:
    DECLARE c_dept CURSOR FOR
        SELECT department_id FROM departments;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET l_last_row=1;

    OPEN c_dept;
    dept_cursor: LOOP
        FETCH c_dept INTO l_dept_id;
        IF (l_last_row=1) THEN
            LEAVE dept_cursor;
        END IF;
    END LOOP dept_cursor;
    CLOSE c_dept;
END;

2，Handlers
语法:

DECLARE {CONTINUE | EXIT} HANDLER FOR
    {SQLSTATE sqlstate_code | MySQL error code | condition_name}
    handler_actions

Handlers类型:

1, EXIT: 发生错误时退出当前代码块（可能是子代码块或者main代码块）
2, CONTINUE: 发送错误时继续执行后续代码

Handlers条件:

1, MySQL error code，如1062
2, ANSI标准SQLSTATE code，如23000
3, 命名条件，如NOT FOUND

优先级：
MySQL Error code > SQLSTATE code > 命名条件

使用SQLSTATE还是MySQL Error Code？
1，SALSTATE是标准，貌似会更portable，但是实际上MySQL、DB2、Oracle等等的存储程序语法大相径庭，所以portable的优势不存在
2，MySQL error code与SQLSTATE并不是一一对应的，比如很多MySQL error code都映射到同一SQLSTATE code(HY000)

当MySQL客户端碰到错误时，它会报告MySQL error code和相关的SQLSATE code:

mysql > CALL nosuch_sp();
ERROR 1305 (42000): PROCEDURE sqltune.nosuch_sp does not exist

上面Error code是1305，SQLSTATE code是42000

常见的MySQL error code和SQLSTATE code:

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

可以在http://dev.mysql.com/doc/的MySQL reference manual的附录B找到完整的最新的error codes

3，命名条件
MySQL error code或者SQLSTATE code的可读性太差，所以引入了命名条件:

DECLARE condition_name CONDITION FOR {SQLSTATE sqlstate_code | MySQL_error_code};

使用:

# original
DECLARE CONTINUE HANDLER FOR 1216 MySQL_statements;

# changed
DECLARE foreign_key_error CONDITION FOR 1216;
DECLARE CONTINUE HANDLER FOR foreign_key_error MySQL_statements;

4，SQL:2003的特性
可以使用SIGNAL语句来触发错误

SIGNAL SQLSTATE sqlstate_code|condition_name [SET MESSAGE_TEXT=string_or_variable];

MySQL5.2才支持 SQL:2003

5，Error Handling的例子

CREATE PROCEDURE sp_add_department
    (p_department_name     VARCHAR(30),
     p_manager_surname     VARCHAR(30),
     p_manager_firstname   VARCHAR(30),
     p_location            VARCHAR(30),
     OUT p_sqlcode         INT,
     OUT p_status_message  VARCHAR(100))
BEGIN

    /* START Declare Conditions */

    DECLARE duplicate_key CONDITION FOR 1062;
    DECLARE foreign_key_violated CONDITION FOR 1216;

    /* END Declare COnditions */

    /* START Declare variables and cursors */

    DECLARE l_manager_id INT;
    DECLARE csr_mgr_id CURSOR FOR
        SELECT employee_id FROM employees
        WHERE surname=UPPER(p_manager_surname)
        AND firstname=UPPER(p_manager_firstname);

    /* END Declare variables and cursors */

    /* START Declare Exception Handlers */

    DECLARE CONTINUE HANDLER FOR duplicate_key
    BEGIN
        SET p_sqlcode=1052;
        SET p_status_message='Duplicate key error';
    END;

    DECLARE CONTINUE HANDLER FOR foreign_key_violated
    BEGIN
        SET p_sqlcode=1216;
        SET p_status_message='Foreign key violated';
    END;

    DECLARE CONTINUE HANDLER FOR NOT FOUND
    BEGIN
        SET p_sqlcode=1329;
        SET p_status_message='No record found';
    END;

    /* END Declare Exception Handlers */

    /* START Execution */

    SET p_sqlcode=0;
    OPEN csr_mgr_id;
    FETCH csr_mgr_id INTO l_manager_id;

    IF p_sqlcode<>0 THEN     /* Failed to get manager id */
        SET p_status_message=CONCAT(p_status_message,' when fetching manager id');
    ELSE                     /* Got manager id, we can try and insert */
        INSERT INTO departments (department_name, manager_id, location)
        VALUES(UPPER(p_department_name), l_manager_id, UPPER(p_location));
        IF p_sqlcode<>0 THEN /* Failed to insert new department */
            SET p_status_message=CONCAT(p_status_message, ' when inserting new department');
        END IF;
    END IF;

    CLOSE csr_mgr_id;

    /* END Execution */

END