Question

我将有一个名为VISIT表的SQL表。

我有3列

工作站，类别，按钮

1,1,1

1,2,3

1,1,2

2,1,1

2,3,1

2,1,2

如何查询该表以获取一个查询语句中每列的不同值？

结果应该是...... ..

工作站，类别，按钮

1,1,1

2,2,2


，3,3

我可以用3个不同的查询来做到这一点。我只是想知道这可以在一个查询中完成，因为这将使程序运行得更快。

Answer 1

尝试使用每列列进行此操作是IMO的一个错误;只需在两列中执行，然后在调用者处选择列：

SELECT DISTINCT 'WS' AS [Col], WORKSTATION AS [Value] FROM VISIT
UNION ALL
SELECT DISTINCT 'CA' AS [Col], CATEGORY AS [Value]  FROM VISIT
UNION ALL
SELECT DISTINCT 'BU' AS [Col], BUTTON AS [Value]  FROM VISIT

与：

或多或少相同

SELECT 'WS' AS [Col], WORKSTATION AS [Value] FROM VISIT
UNION
SELECT 'CA' AS [Col], CATEGORY AS [Value]  FROM VISIT
UNION
SELECT 'BU' AS [Col], BUTTON AS [Value]  FROM VISIT

这是一次往返等等。我可能会对第一列使用整数（甚至可能是tinyint）（客户端应该知道1映射到WORKSTATION等）而不是varchar，但上面只给出了味道。

编辑评论;以下考虑到：

在联合中包含不同的数据类型（转换为通用类型）
对原始数据使用序数排序，因此整数仍然是1,2,10（整数排序），而不是1,10,2（字符串排序）

TSQL：

DECLARE @VISIT TABLE (WORKSTATION int, CATEGORY varchar(10), BUTTON int)
INSERT @VISIT VALUES (1,'1',1)
INSERT @VISIT VALUES (1,'2',3)
INSERT @VISIT VALUES (2,'1',2)
INSERT @VISIT VALUES (10,'1',1)
INSERT @VISIT VALUES (10,'3',1)
INSERT @VISIT VALUES (10,'1',2)

SELECT x.Col, x.Value
FROM (
  SELECT CAST(1 as tinyint) AS [Col], ROW_NUMBER() over(order by WORKSTATION)
    AS [Sort], CONVERT(varchar(20), WORKSTATION) AS [Value] FROM @VISIT
  UNION
  SELECT CAST(2 as tinyint) AS [Col], ROW_NUMBER() over(order by CATEGORY)
    AS [Sort], CATEGORY AS [Value] FROM @VISIT
  UNION
  SELECT CAST(3 as tinyint) AS [Col], ROW_NUMBER() over (order by BUTTON)
    AS [Sort], CONVERT(varchar(20), BUTTON) AS [Value] FROM @VISIT
) x ORDER BY x.Col, x.Sort

Answer 2

一些想法......

两个完整的外部联接：

SELECT DISTINCT w.workstation, c.category, b.button
  FROM VISIT w FULL OUTER JOIN VISIT c ON (w.workstation = c.category)
  FULL OUTER JOIN VISIT b ON (w.workstation = b.button OR c.category = b.button)

VISIT的子查询也可能加快速度：

SELECT w.workstation, c.category, b.button
FROM (SELECT DISTINCT workstation FROM VISIT) w 
FULL OUTER JOIN (SELECT DISTINCT category FROM VISIT) c 
             ON (w.workstation = c.category)
FULL OUTER JOIN (SELECT DISTINCT button FROM VISIT) b 
             ON (w.workstation = b.button OR c.category = b.button)

如果您愿意，可以订购：

ORDER BY COALESCE(w.workstation, c.category, b.button)

来自同一表的3个不同的不同值

2 个答案: