Question

What I would like to do is to run a where clause only if a certain value (that will be loaded dynamically) = a certain value. For example

IF ('<=' == '$dynamic_value') THEN WHERE...

Is this possible? (the $dynamic value will either be <=, or >=)

In other words, I would like to use the where clause only when certain value happens or invoke.

Answer 1

You can use a CASE expression in the WHERE clause like so:

SELECT *
FROM tbl
WHERE 
    CASE '$dynamic_value' 
        WHEN '>=' THEN column_a >= column_b AND other_conditions
        WHEN '<=' THEN column_a <= column_b AND other_conditions
        ELSE 1
    END

If $dynamic_value does not equal to either >= or <=, the ELSE 1 will be used by the WHERE clause instead – which is basically like having no WHERE clause at all (and return all records).

Since it seems like you’re using PHP and the value of $dynamic_value can only be >= or <=, you can just insert the parameter directly like:

$sql = "
    SELECT *
    FROM tbl
    WHERE column_a $dynamic_value column_b";

Of course if coming from user-input, then be sure you’re checking whether $dynamic_value is either >= or <=.