Introduction to Error Handling
Let’s begin by looking at several examples of stored program error handling.
A Simple First Example
Consider a simple stored procedure that creates a location record, as shown in Example 6-1.
CREATE PROCEDURE sp_add_location (in_location VARCHAR(30), in_address1 VARCHAR(30), in_address2 VARCHAR(30), zipcode VARCHAR(10)) MODIFIES SQL DATA BEGIN INSERT INTO locations (location,address1,address2,zipcode) VALUES (in_location,in_address1,in_address2,zipcode); END$$
This procedure works fine when the location does not already exist, as shown in the following output:
mysql> CALL sp_add_location('Guys place','30 Blakely Drv', 'Irvine CA','92618-20'); Query OK, 1 row affected, 1 warning (0.44 sec)
However, if we try to insert a department that already exists, MySQL raises an error:
mysql> CALL sp_add_location('Guys place','30 Blakely Drv', 'Irvine CA','92618-20'); ERROR 1062 (23000): Duplicate entry 'Guys place' for key 1
If the stored procedure is called by an external program such as PHP, we could probably get away with leaving this program “as is.” PHP, and other external programs, can detect such error conditions and then take appropriate action. If the stored procedure is called from another stored procedure, however, we risk causing the entire procedure call stack to abort. That may not be what we want.
Since we can anticipate that MySQL error 1062 could be raised by this procedure, we can write code ...