如何從MySQL中的CASE狀態獲取結果？

Question

SELECT field_name, 
SUM(CASE WHEN field_name is not null THEN 1 ELSE 0 END) as count from table_name group by department 


RESULT IS: 

field_name count 

AAA    9 
BBB    0 
CCC    7 

但是我怎樣才能得到只有在第二列有更多0的行。

Answer 1

SELECT field_name, 
     SUM(CASE WHEN field_name is not null 
        THEN 1 
        ELSE 0 
      END) as count 
    from table_name 
group by department 
    HAVING `count` > 0 

HAVING子句後WHERE和GROUP BY執行從而可以解決聚合函數

Answer 2

使用HAVING條款：

SELECT field_name, 
    SUM(CASE WHEN field_name IS NOT NULL 
       THEN 1 ELSE 0 END) AS `count` 
    FROM table_name 
GROUP BY department 
    HAVING `count` > 0 

_{我覺得你選擇，而不是field_name或者你department需要分組field_name}

Answer 3

請嘗試以下。

SELECT field_name, SUM(CASE WHEN field_name is not null THEN 1 ELSE 0 END) as count 
from table_name 
where field_name is not null 

實際上，第二個查詢是很好理解的，但第一個查詢是更好:)

SELECT field_name, SUM(CASE WHEN field_name is not null THEN 1 ELSE 0 END) as count 
from table_name 
where SUM(CASE WHEN field_name is not null THEN 1 ELSE 0 END) > 0