Question

Does FROM_UNIXTIME heavily affect the performance of a query like this:

        (
            (calltasks.task_dueDate = '".$date."') # Tasks of this date
            OR 
            (calltasks.task_dueDate < '".$date."' AND calltasks.task_status = 'scheduled') # Tasks still available on this date
            OR 
            (FROM_UNIXTIME(calltasks.task_executionTime, '%Y-%m-%d') = '".$date."') # Tasks finished this date
        )

Or I should be fine with it ??

Answer 1

Rather than converting your UNIX time to a formatted string, then comparing those (as you currently are), you would be better to use UNIX_TIMESTAMP() to convert your $date variable to a UNIX time and then compare integers (checking the difference is no more than 24 hours). Integer comparison will always be faster than string comparison:

(calltasks.task_executionTime - UNIX_TIMESTAMP('$date')) BETWEEN 0 AND 86400

Alternatively, you may find that you already have the UNIX timestamp value of $date somewhere readily available in the language from which you are invoking this query: PHP, for example, stores dates as UNIX timestamps.

Note that you should be absolutely certain that $date cannot be manipulated to contain SQL if you are inserting it into your query in this fashion; if there is any doubt, you should use a prepared statement: if you don’t know why, or what they are, read about Bobby Tables.