如何通过不使用 union all 来更改 SQL 查询答案

【问题标题】：how to change SQL query by not using union all如何通过不使用 union all 来更改 SQL 查询
【发布时间】：2017-11-02 22:09:42
【问题描述】：

这是桌子

table table_nm(
ID
,AA
,BB
)

而且，这是我想要更改的查询

select
COUNT(DISTINCT(ID)) AS ID_AA
, AA as AA_1
, 0 as ID_BB
, 0 as BB_1 
from table_nm
group by
AA

UNION ALL

select
  0 as ID_AA
, 0 as AA_1
, COUNT(DISTINCT(ID)) AS ID_BB
, BB as BB_1
from table_nm
group by
BB

如何在没有 UNION ALL 的情况下更改该查询？

【问题讨论】：

您好，我不知道您的具体要求是什么。请查看这些可能有帮助的链接：- stackoverflow.com/questions/7053471/… technet.microsoft.com/en-us/library/bb522495(v=sql.105).aspx
UNION ALL 有什么问题？
DISTINCT 不是函数。您可以删除那些多余的括号以使事情更清楚。（即COUNT(DISTINCT ID)。）

标签： sql sql-server database union-all

【解决方案1】：

我猜你正在寻找这样的东西。

SELECT L.ID_AA, L.AA_1, R.ID_BB, R.BB_1 
FROM ( 
    select
    COUNT(DISTINCT(ID)) AS ID_AA
    , AA as AA_1
    , 0 as ID_BB
    , 0 as BB_1 
    from table_nm
    group by AA
) AS L
FULL JOIN
(
    select
      0 as ID_AA
    , 0 as AA_1
    , COUNT(DISTINCT(ID)) AS ID_BB
    , BB as BB_1
    from table_nm
    group by BB
) AS R ON L.AA_1 = R.BB_1

【讨论】：

【解决方案2】：

您可以像这样使用GROUPING SETS 和GROUPING_ID

SELECT 
       CASE WHEN grouping_ID(tn.AA) = 0 THEN tn.AA ELSE 0 END AS AA_1,
       CASE WHEN grouping_ID(tn.AA) = 0 THEN count(DISTINCT(tn.ID)) ELSE 0 END AS ID_AA,
       CASE WHEN grouping_ID(tn.BB) = 0 THEN tn.BB ELSE 0 END AS BB_1,
       CASE WHEN grouping_ID(tn.BB) = 0 THEN count(DISTINCT(tn.ID)) ELSE 0 END  AS ID_BB
FROM @table_nm tn
GROUP BY GROUPING SETS ((tn.AA),(tn.BB))

在这里查看演示http://rextester.com/SWN42877

【讨论】：

【解决方案3】：

您将能够使用以下查询。

SELECT t1.AA_1,
       t1.ID_AA,
       t2.BB_1,
       t2.ID_BB
FROM
(
    SELECT AA AS AA_1,
           COUNT(DISTINCT ID) AS ID_AA
    FROM table_nm
    GROUP BY AA
) t1
FULL OUTER JOIN
(
    SELECT BB AS BB_1,
           COUNT(DISTINCT ID) AS ID_BB
    FROM table_nm
    GROUP BY BB
) t2 ON t1.AA_1 = t2.BB_1;

为了获得空值 0，您可以分别对 MySQL、SQL Server 和 Oracle 使用 COALESCE()（即标准 ANSI SQL）、IFNULL、ISNULL 或 NVL 函数。

【讨论】：

DISTINCT 不是函数。您可以删除那些多余的括号以使事情更清楚。（即COUNT(DISTINCT ID)）
COALESCE() 是返回第一个非空参数的通用函数。