MySQL Stored Procedure Programming

Name

IF-02: Use IF...ELSEIF only to test a single, simple condition

Synopsis

The real world is very complicated; the software we write is supposed to map those complexities into applications. The result is that we often end up needing to deal with convoluted logical expressions.

You should write your IF statements in such a way as to keep them as straightforward and understandable as possible. For example, expressions are often more readable and understandable when they are stated in a positive form. Consequently, you are probably better off avoiding the NOT operator in conditional expressions.

Example

It's not at all uncommon to write or maintain code that is structured like this:

    IF condA AND NOT (condB OR condC) THEN
       CALL proc1;
    ELSEIF condA AND (condB OR condC) THEN
       CALL proc2;
    ELSEIF NOT condA AND condD THEN
       CALL proc3;
    END IF;

It's also fairly common to get a headache trying to make sense of all of that. You can often reduce the trauma by trading off the simplicity of the IF statement itself (one level of IF and ELSEIF conditions) for the simplicity of clauses within multiple levels:

    IF condA THEN
       IF (condB OR condC)    THEN
         CALL  proc2;
       ELSE
         CALL  proc1;
       END IF;
    ELSEIF condD THEN
       CALL proc3
    END IF;

Don't forget, by the way, to take into account the possibility of your expressions evaluating to NULL. This can throw a monkey wrench into your conditional processing.

Benefits

Following this best practice will make your code easier to read and maintain.

Breaking an expression into smaller pieces ...