Question

This is what I would like to be able to do:

SET @interval_type := MONTH;
SELECT '2012-01-01' + INTERVAL 6 @interval_type;
+------------+
|'2012-06-01'|
+------------+

And of course that doesn’t work and there is no “interval” data type in MySQL.

I want to be able to store an interval value and an interval type in a table so that i can have the database quickly do the math naturally without having to write a big switch statement, ala

... ELSE IF (type = 'MONTH') { SELECT @date + INTERVAL @value MONTH; } ... 

Is this supported in any way in MySQL or do you have a clever hack for this?

Thanks; you rock.

Answer 1

Here’s the simplistic approach. It works reasonably fast. You can change the order of the switch statements to optimize for speed if you feel that you will be hitting some more often then others. I have not benched this against Chris Hutchinson’s solution. I ran into problems trying to wrap it into a nice function because of the dynamic SQL. Anyway, for posterity, this is guaranteed to work:

CREATE FUNCTION AddInterval( date DATETIME, interval_value INT, interval_type TEXT  ) 
RETURNS DATETIME
DETERMINISTIC
BEGIN
    DECLARE newdate DATETIME;
    SET newdate = date;

    IF interval_type = 'YEAR' THEN
        SET newdate = date + INTERVAL interval_value YEAR;
    ELSEIF interval_type = 'QUARTER' THEN
        SET newdate = date + INTERVAL interval_value QUARTER;
    ELSEIF interval_type = 'MONTH' THEN
        SET newdate = date + INTERVAL interval_value MONTH;
    ELSEIF interval_type = 'WEEK' THEN
        SET newdate = date + INTERVAL interval_value WEEK;
    ELSEIF interval_type = 'DAY' THEN
        SET newdate = date + INTERVAL interval_value DAY;
    ELSEIF interval_type = 'MINUTE' THEN
        SET newdate = date + INTERVAL interval_value MINUTE;
    ELSEIF interval_type = 'SECOND' THEN
        SET newdate = date + INTERVAL interval_value SECOND;
    END IF;

    RETURN newdate;
END //

It comes with this equally simplistic benchmark test:

CREATE FUNCTION `TestInterval`( numloops INT ) 
RETURNS INT
DETERMINISTIC
BEGIN
    DECLARE date DATETIME;
    DECLARE newdate DATETIME;
    DECLARE i INT; 
    SET i = 0;

    label1: LOOP
        SET date = FROM_UNIXTIME(RAND() * 2147483647);
        SET newdate = AddInterval(date,1,'YEAR');
        SET i = i+1;
        IF i < numloops THEN
            ITERATE label1;
        ELSE
            LEAVE label1;
        END IF;
    END LOOP label1;
    return i;
END //