Question

我在SQL中有一个查询，该查询对值求和并将其添加为日期的月份。

    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;

当这些总和中的某些值为空而不是0且我无法更改数据源时，就会出现问题。

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

由于(C.items_left + C.items_given)为空，所以会生成空。

所以，问题是，我该如何执行该总和以使结果为0而不是null？

Answer 1

使用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)

SQL将空值的总和转换为0

2 个答案: