MySQL 如何在MySQL存储过程里处理结果集？

我们可以使用游标来处理存储过程中的结果集。基本上，游标允许我们迭代由查询返回的若干行，并相应处理每一行。

为了演示在MySQL存储过程中使用CURSOR，我们创建了以下存储过程，其基于表student_info的如下值-

mysql> Select * from student_info;
+-----+---------+----------+------------+
| id  | Name    | Address  | Subject    |
+-----+---------+----------+------------+
| 101 | YashPal | Amritsar | History    |
| 105 | Gaurav  | Jaipur   | Literature |
| 125 | Raman   | Shimla   | Computers  |
+-----+---------+----------+------------+
3 rows in set (0.00 sec)

以下查询将创建一个名为’list_address’的过程，该过程返回存储在表中的所有地址列表 –

mysql> Delimiter //
mysql> CREATE PROCEDURE list_address (INOUT address_list varchar(255))
    -> BEGIN
    -> DECLARE value_finished INTEGER DEFAULT 0;
    -> DECLARE value_address varchar(100) DEFAULT "";
    -> DEClARE address_cursor CURSOR FOR
    -> SELECT address FROM student_info;
    -> DECLARE CONTINUE HANDLER
    -> FOR NOT FOUND SET value_finished = 1;
    -> OPEN address_cursor;
    -> get_address: LOOP
    -> FETCH address_cursor INTO value_address;
    -> IF value_finished = 1 THEN
    -> LEAVE get_address;
    -> END IF;
    -> SET address_list = CONCAT(value_address,";",address_list);
    -> END LOOP get_address;
    -> CLOSE address_cursor;
    -> END //
Query OK, 0 rows affected (0.00 sec)

现在，我们调用此过程时可以看到以下结果 –

mysql> DELIMITER ;

mysql> Set @address_list = "";
Query OK, 0 rows affected (0.00 sec)

mysql> CALL list_address(@address_list);
Query OK, 0 rows affected (0.00 sec)

mysql> Select @address_list;
+-------------------------+
| @address_list           |
+-------------------------+
| Shimla;Jaipur;Amritsar; |
+-------------------------+
1 row in set (0.00 sec)

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