Sql如果一列返回null，则整个结果集为null

Question

我有一个问题：

select 'False' as COL_1, coalesce(sum(volume),0) as COL_2 
from table1
where eligible like 'False%' and Month = :month

基本上我正在创建第一列来读取False以及找到了什么结果，我的问题是如果我的col_2返回null，那么它仍会在结果中显示col_1 false。

我想要它，以便如果col_2返回null，整个查询返回null，我一直在玩coalesce，notnull，ifnull等......无济于事。

感谢任何帮助！

Answer 1

SELECT IF(SUM(volume) = 0, NULL, 'False') AS COL_1, SUM(volume) AS COL_2 ...

Answer 2

SELECT CASE WHEN (coalesce(sum(volume),0)) IS NULL
            THEN NULL
            ELSE 'False' 
       END AS COL_1, 
       coalesce(sum(volume),0) AS COL_2 
FROM table1 
WHERE eligible LIKE 'False%' AND Month = :month

Answer 3

select 'False' as COL_1, sum(volume) as COL_2 
from table1 where eligible like 'False%' and Month = :month  
having sum(volume) is not null

sum是一个聚合函数。如果要在聚合结果上添加where条件，则必须在select的having子句部分中定义它。

当我们过滤sum（volume）= null的情况时，不再需要合并。