MySQL Stored Procedure Programming

Named Conditions

So far, our examples have used conditions based on MySQL error codes, SQLSTATE codes, or predefined named conditions (SQLEXCEPTION, SQLWARNING, NOT FOUND). These handlers do the job required, but they do not result in particularly readable code, since they rely on the hardcoding of literal error numbers. Unless you memorize all or most of the MySQL error codes and SQLSTATE codes (and expect everyone maintaining your code to do the same), you are going to have to refer to a manual to understand exactly what error a handler is trying to catch.

You can improve the readability of your handlers by defining a condition declaration, which associates a MySQL error code or SQLSTATE code with a meaningful name that you can then use in your handler declarations. The syntax for a condition declaration is:

    DECLARE condition_name CONDITION FOR {SQLSTATE sqlstate_code | MySQL_error_code};

Once we have declared our condition name, we can use it in our code instead of a MySQL error code or SQLSTATE code. So instead of the following declaration:

    DECLARE CONTINUE HANDLER FOR 1216 MySQL_statements;

we could use the following more readable declaration:

    DECLARE foreign_key_error CONDITION FOR 1216;

    DECLARE CONTINUE HANDLER FOR foreign_key_error MySQL_statements;

Tip

Create named conditions using condition declarations, and use these named conditions in your handlers to improve the readability and maintainability of your stored program code.