SQL将空值的总和转换为0

Question

I have a query in SQL which sum values and add them as months to a date.

    SELECT
    FROM_UNIXTIME(S.created) as start_date, 
   (FROM_UNIXTIME(S.created) + INTERVAL (C.items_left + C.items_given) MONTH)
    AS end_date,
    FROM table1 S
    LEFT JOIN table2 C ON C.id = S.id;

The problem arises when some of these values to sum are null instead of 0 and I am not able to change the source of data.

(FROM_UNIXTIME(S.created) + INTERVAL (C.items_left + C.items_given) MONTH)
AS end_date,

is generating nulls because (C.items_left + C.items_given) is null.

So, the question is, how do I execute this sum so the result is 0 instead of null?

Answer 1

use coalesce

SELECT
    FROM_UNIXTIME(S.created) as start_date, 
   ( coalesce(FROM_UNIXTIME(S.created),0) + INTERVAL coalesce((coalesce(C.items_left,0) + coalesce(C.items_given,0)),0) MONTH)
    AS end_date,
    FROM table1 S
    LEFT JOIN table2 C ON C.id = S.id;

Answer 2

使用COALESCE() ：

(FROM_UNIXTIME(S.created) + INTERVAL (COALESCE(C.items_left, 0) + COALESCE(C.items_given, 0)) MONTH)