mariadb UNION select如何返回两列而不是一行？答案

【问题标题】：mariadb UNION select how to return two columns insted of one row?mariadb UNION select如何返回两列而不是一行？
【发布时间】：2021-06-18 15:49:46
【问题描述】：

我在 mariadb 中有以下查询：

SELECT
MONTHNAME (itd.DateOfshippment) AS Month
-- COUNT(itm.Name) AS Operations
FROM ImportsMaster itm
INNER JOIN ImportsDetails itd on itm.ID  = itd.IDMSTR 
WHERE itd.Market IS NOT NULL 
AND itm.Trader LIKE "%TEXT%"
AND itd.DateOfshippment between '2020-08-29' and '2020-12-31'
GROUP BY MONTH(itd.DateOfshippment)

如果我取消注释 COUNT 子句并注释每个查询返回的 MONTHNAME 子句一组相关的数据，例如：

问：

Month
Jan 
Feb
March
Apr

和Qb：

Operations
3
4
2
4

我尝试了各种方法让查询返回使用 UNION 的单个查询，例如：

SELECT
    MONTHNAME (itd.DateOfshippment) AS Month
    -- COUNT(itm.Name) AS Operations
    FROM ImportsMaster itm
    INNER JOIN ImportsDetails itd on itm.ID  = itd.IDMSTR 
    WHERE itd.Market IS NOT NULL 
    AND itm.Trader LIKE "%TEXT%"
    AND itd.DateOfshippment between '2020-08-29' and '2020-12-31'
    GROUP BY MONTH(itd.DateOfshippment)
UNION SELECT
    -- MONTHNAME (itd.DateOfshippment) AS Month
    COUNT(itm.Name) AS Operations
    FROM ImportsMaster itm
    INNER JOIN ImportsDetails itd on itm.ID  = itd.IDMSTR 
    WHERE itd.Market IS NOT NULL 
    AND itm.Trader LIKE "%TEXT%"
    AND itd.DateOfshippment between '2020-08-29' and '2020-12-31'
    GROUP BY MONTH(itd.DateOfshippment)

但我得到的是单列结果，例如：

Month
Jan 
Feb
March
Apr 
3
4
2
4

有没有办法获得两列的结果？我在这里做错了什么？

谢谢

【问题讨论】：

标签： mysql sql mariadb

【解决方案1】：

不确定您为什么要为此尝试使用UNION。如果有必要，其他答案很有帮助。只需在同一个查询中选择两者即可获得两列。

SELECT
MONTHNAME (itd.DateOfshippment) AS Month
,COUNT(itm.Name) AS Operations
FROM ImportsMaster itm
INNER JOIN ImportsDetails itd on itm.ID  = itd.IDMSTR 
WHERE itd.Market IS NOT NULL 
AND itm.Trader LIKE "%TEXT%"
AND itd.DateOfshippment between '2020-08-29' and '2020-12-31'
GROUP BY MONTH(itd.DateOfshippment)

【讨论】：

哇，我已经尝试过同样的方法，但没有添加逗号，这是我的一个愚蠢的错误！男人有时候是那么的难看。我没有查看代码，而是尝试了各种愚蠢的 UNION CASE 等。谢谢！！

【解决方案2】：

您将选择两列：

SELECT MONTHNAME (itd.DateOfshippment) AS Month, NULL as Operations
FROM ImportsMaster itm JOIN
     ImportsDetails itd 
     ON itm.ID  = itd.IDMSTR 
WHERE itd.Market IS NOT NULL AND
      itm.Trader LIKE '%TEXT%' AND
      itd.DateOfshippment between '2020-08-29' and '2020-12-31'
GROUP BY MONTH(itd.DateOfshippment)
UNION ALL
SELECT NULL AS Month,
       COUNT(itm.Name) AS Operations
FROM ImportsMaster itm JOIN
     ImportsDetails itd 
     ON itm.ID = itd.IDMSTR 
WHERE itd.Market IS NOT NULL AND
      itm.Trader LIKE '%TEXT%' AND
      itd.DateOfshippment between '2020-08-29' and '2020-12-31'
GROUP BY MONTH(itd.DateOfshippment);

为什么你会想这样做让我很困惑。

【讨论】：

这是第二次接近解决方案，唯一的麻烦是它在每个响应列中添加了 NULLS。无论如何，谢谢。

【解决方案3】：

UNION ALL 将选择第一个查询中的所有行，并将第二个查询中的行添加到该结果中。

您可以这样做（或简单地选择两个字段，然后在 1 个查询中进行）：

SELECT 
  query1.Month, 
  query2.Operations,
FROM (
  SELECT
    MONTHNAME (itd.DateOfshippment) AS Month,
    -- COUNT(itm.Name) AS Operations
    row_number() over (order by MONTH(itd.DateOfshippment)) as r
    FROM ImportsMaster itm
    INNER JOIN ImportsDetails itd on itm.ID  = itd.IDMSTR 
    WHERE itd.Market IS NOT NULL 
    AND itm.Trader LIKE "%TEXT%"
    AND itd.DateOfshippment between '2020-08-29' and '2020-12-31'
    GROUP BY MONTH(itd.DateOfshippment)
) query1
cross join (
    -- MONTHNAME (itd.DateOfshippment) AS Month
    COUNT(itm.Name) AS Operations,
    row_number() over (order by MONTH(itd.DateOfshippment)) as r
    FROM ImportsMaster itm
    INNER JOIN ImportsDetails itd on itm.ID  = itd.IDMSTR 
    WHERE itd.Market IS NOT NULL 
    AND itm.Trader LIKE "%TEXT%"
    AND itd.DateOfshippment between '2020-08-29' and '2020-12-31'
    GROUP BY MONTH(itd.DateOfshippment)
) query2
where query1.r = query2.r

【讨论】：