MySQL 如何创建存储过程以基于某些条件从MySQL表中选择值？

我们可以使用IN和OUT操作符创建一个存储过程来根据某些条件从MySQL表中选择记录。为了使其易于理解，我们以一个名为“student_info”的表为例，该表具有以下数据 –

mysql> Select * from student_info;
+------+---------+------------+------------+
| id   | Name    | Address    | Subject    |
+------+---------+------------+------------+
| 101  | YashPal | Amritsar   | History    |
| 105  | Gaurav  | Jaipur     | Literature |
| 110  | Rahul   | Chandigarh | History    |
| 125  | Raman   | Bangalore  | Computers  |
+------+---------+------------+------------+
4 rows in set (0.01 sec)

现在，通过创建名为‘select_studentinfo’的过程，我们可以提供‘id’的值来从‘student_info’表中选择值 –

mysql> DELIMITER // ;
mysql> Create Procedure Select_studentinfo ( IN p_id INT, OUT p_name varchar(20),OUT p_address varchar(20), OUT p_subject varchar(20))
   -> BEGIN
   -> SELECT name, address, subject INTO p_name, p_address, p_subject
   -> FROM student_info
   -> WHERE id = p_id;
   -> END //
Query OK, 0 rows affected (0.03 sec)

现在，使用我们要提供为条件的值调用该过程，如下所示 –

mysql> DELIMITER ; //
mysql> CALL Select_studentinfo(110, @p_name, @p_address, @p_subject);
Query OK, 1 row affected (0.06 sec)

mysql> Select @p_name AS Name,@p_Address AS Address, @p_subject AS Subject;
+--------+------------+-----------+
| Name   | Address    | Subject   |
+--------+------------+-----------+
| Rahul  | Chandigarh | History   |
+--------+------------+-----------+
1 row in set (0.00 sec)

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