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How do I avoid the variable value in a MySQL stored procedure to change when records are updated?


1 Answer
Ankith Reddy

We will create a stored procedure that does not change the variable value whenever the value is updated.

Let us first create a table −

mysql> create table DemoTable
   (
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   Value int
   );
Query OK, 0 rows affected (0.63 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable(Value) values(100);
Query OK, 1 row affected (0.13 sec)
Display all records from the table using select statement :
mysql> select *from DemoTable;

Output

+----+-------+
| Id | Value |
+----+-------+
| 1 | 100    |
+----+-------+
1 row in set (0.00 sec)

Following is the stored procedure that shows the old value after updating −

mysql> DELIMITER //
   mysql> CREATE PROCEDURE updateValue100()
   BEGIN
      DECLARE myValue int;
      select @myValue :=(select Value from DemoTable where Id=1);
      select @myValue;
      update DemoTable set Value=200 where Id=1;
      select @myValue :=(select Value from DemoTable where Id=1);
      select @myValue;
   END
   //
   Query OK, 0 rows affected (0.21 sec)
mysql> DELIMITER ;

Now you can call the stored procedure using CALL command −

mysql> call updateValue100();

Output

+-------------------------------------------------------+
| @myValue :=(select Value from DemoTable where Id=1)   |
+-------------------------------------------------------+
| 100                                                   |
+-------------------------------------------------------+
1 row in set (0.00 sec)
+----------+
| @myValue                                              |
+----------+
| 100                                                   |
+----------+
1 row in set (0.01 sec)
+-------------------------------------------------------+
| @myValue :=(select Value from DemoTable where Id=1)   |
+-------------------------------------------------------+
| 200                                                   |
+-------------------------------------------------------+
1 row in set (0.16 sec)
+----------+
| @myValue |
+----------+
| 200      |
+----------+
1 row in set (0.17 sec)
Query OK, 0 rows affected (0.18 sec)

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