How to Implement Conditional Logic in MySQL SELECT Queries?

IF Statements in MySQL SELECT Queries

When trying to use an IF statement in a MySQL SELECT query, it's important to understand the limitations of IF statements in MySQL.

In MySQL, the IF/THEN/ELSE construct is only valid within stored procedures and functions. Therefore, the provided query will not execute correctly due to the use of the IF/THEN/ELSE statement in the WHERE clause.

To handle conditional statements in a SELECT query, the IF() function can be used, but its functionality differs from the IF/THEN/ELSE construct. The IF() function evaluates a condition and returns a specified value if true or a different value if false. It is primarily used in the SELECT clause to dynamically select data based on certain conditions. For example:

SELECT IF(JQ.COURSE_ID=0, 'Some Result If True', 'Some Result If False'), OTHER_COLUMNS
FROM ...
WHERE ...

However, the IF() function cannot be used to control the flow of the WHERE clause as in the example query. To achieve the desired functionality, consider restructuring the query to use multiple nested WHERE clauses or CASE statements to evaluate the conditions.

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