Evaluating truthy values

Question

I wanted to say something like:

 if field_1 then set field_2 = 1

Meaning, if field_1 holds a truthy value, do something else. Can an IF statement in sql execute this kind of evaluation?

What should `field_2` be set to otherwise - if `field_1` is falsy? — gen_Eric, Oct 10 '16 at 16:36
@RocketHazmat I guess my question just has to do more with whether or not I can make a truthy evaluation, and not the syntax of an if then else statement. — Joseph Erickson, Oct 10 '16 at 16:37
You could try it with the [`IF()` function](http://dev.mysql.com/doc/refman/5.5/en/control-flow-functions.html#function_if). Something like: `SET field_2 = IF(field_1, 1, 0)`. — gen_Eric, Oct 10 '16 at 16:38
have you just tried a simple google search for this? there are plenty of results!! :) — Lelio Faieta, Oct 10 '16 at 16:40
@LelioFaieta I have googled "truthy values" extensively. Not a lot of material. — Joseph Erickson, Oct 10 '16 at 16:42
@LelioFaieta not a duplicate because my question has nothing to do with output columns and everything to do with a truthy evaluation. — Joseph Erickson, Oct 10 '16 at 16:42
Maybe "MySQL if statements "? Or "MySQL conditional statements "? — Lelio Faieta, Oct 10 '16 at 16:43
@LelioFaieta this has nothing to do with conditional statements — Joseph Erickson, Oct 10 '16 at 16:47

score 2 · Accepted Answer · answered Oct 10 '16 at 16:39

2

Use CASE WHEN THEN and set field2 to 1 if the CASE WHEN is true, else use ELSE to set field2 to what it was before.

UPDATE table 
SET field2 = CASE
WHEN field1 IS NOT NULL 
THEN 1
ELSE field2
END;

answered Oct 10 '16 at 16:39

baao

this is a really nice way to do this, and I was familiar with IS NOT NULL, so I guess you can't make a truthy evaluation? – Joseph Erickson Oct 10 '16 at 16:43
Everything but null is true in mysql @JosephErickson – baao Oct 10 '16 at 16:44
@JosephErickson if you wan't to check against the string `true` or `1`, simply replace `is not null` with `=1` or `='true'` – baao Oct 10 '16 at 16:45

1 Answers1