Question

Is it possible to check if num rows in a table is 0 then perform an insert, all in ONE sql statement?

Here’s my query that I tried but it says I have a syntax error:

$query = 
    "IF (SELECT COUNT(ID) FROM votes WHERE userid = $userid AND itemid = $itemid AND itemtype=1) = 0
        INSERT INTO votes (itemtype, itemid, userid) VALUES (1, $itemid, $userid) 
        SELECT 1 AS result
    ELSE
        SELECT 0 AS result
    END IF";

I know the SELECT COUNT bit works successfully on its own.

Answer 1

NO IDEA if this is the best way of solving this, but it will work. Basically, it simply causes an error if the condition is false, and so it prevents insert:

-- make itemtype not nullable then simply insert
INSERT INTO votes SELECT
   CASE
      WHEN 
        (SELECT COUNT(ID) 
         FROM votes 
         WHERE userid = $userid AND itemid = $itemid AND itemtype=1) = 0 THEN 1
      ELSE NULL
    END CASE,
    $itemid, $userid;