上次说到，既然有Pivot 的行转列，那么肯定也有Unpivot 的列转行 。其实unpivot 处理的情况也是差不多，也是分3步走。
首先也是先演示一下unpivot 的用法
CREATE TABLE #Emp (Name NVARCHAR(50),Mon TIME,Tue TIME,Wed TIME,Thu TIME) INSERT INTO #Emp
( Name, Mon, Tue, Wed, Thu )
VALUES ( N'Ken', '8:30', '8:45','9:05','8:55' ),
( N'Joan', '8:25', '8:35', NULL,'9:00' ),
( N'Jack', '8:15', '9:03','9:05','8:38' ),
( N'Bob', '9:30', '8:53','9:01','8:56' ) SELECT * FROM #Emp Name Mon Tue Wed Thu
-------------------------------------------------- ---------------- ---------------- ---------------- ----------------
Ken 08:30:00.0000000 08:45:00.0000000 09:05:00.0000000 08:55:00.0000000
Joan 08:25:00.0000000 08:35:00.0000000 NULL 09:00:00.0000000
Jack 08:15:00.0000000 09:03:00.0000000 09:05:00.0000000 08:38:00.0000000
Bob 09:30:00.0000000 08:53:00.0000000 09:01:00.0000000 08:56:00.0000000
SELECT *
FROM #Emp UNPIVOT( [LoginTime] FOR [WeekDay] IN (Mon,Tue,Wed,Thu)) a Name LoginTime WeekDay
-------------------------------------------------- ---------------- --------------------------------------------------------------------------------------------------------------------------------
Ken 08:30:00.0000000 Mon
Ken 08:45:00.0000000 Tue
Ken 09:05:00.0000000 Wed
Ken 08:55:00.0000000 Thu
Joan 08:25:00.0000000 Mon
Joan 08:35:00.0000000 Tue
Joan 09:00:00.0000000 Thu
Jack 08:15:00.0000000 Mon
Jack 09:03:00.0000000 Tue
Jack 09:05:00.0000000 Wed
Jack 08:38:00.0000000 Thu
Bob 09:30:00.0000000 Mon
Bob 08:53:00.0000000 Tue
Bob 09:01:00.0000000 Wed
Bob 08:56:00.0000000 Thu
解释一下，
UNPIVOT( [LoginTime] FOR [WeekDay] IN (Mon,Tue,Wed,Thu)) 里面 。 WeekDay 是 根据 (Mon,Tue,Wed,Thu) 这4个列聚合起来的新列的名称，而 LoginTime 呢，就是存放 (Mon,Tue,Wed,Thu) 这几个列下面的值的新列名称。用起来还是挺方便的。
然后下面我要讲一下unpivot 的3步新路里程
1、赋值元素。首先是会按照 (Mon,Tue,Wed,Thu ) 4个列进行一个行赋值。生成第一步的虚拟表。就像下面一样
SELECT *
FROM #Emp a
FULL JOIN (SELECT 'Mon' AS [WeekDay]
UNION ALL
SELECT 'Tue' AS [WeekDay]
UNION ALL
SELECT 'Wed' AS [WeekDay]
UNION ALL
SELECT 'Thu' AS [WeekDay])b ON 1 = 1 得出中间表
Name Mon Tue Wed Thu WeekDay
-------------------------------------------------- ---------------- ---------------- ---------------- ---------------- -------
Bob 09:30:00.0000000 08:53:00.0000000 09:01:00.0000000 08:56:00.0000000 Mon
Bob 09:30:00.0000000 08:53:00.0000000 09:01:00.0000000 08:56:00.0000000 Tue
Bob 09:30:00.0000000 08:53:00.0000000 09:01:00.0000000 08:56:00.0000000 Wed
Bob 09:30:00.0000000 08:53:00.0000000 09:01:00.0000000 08:56:00.0000000 Thu
Jack 08:15:00.0000000 09:03:00.0000000 09:05:00.0000000 08:38:00.0000000 Thu
Jack 08:15:00.0000000 09:03:00.0000000 09:05:00.0000000 08:38:00.0000000 Wed
Jack 08:15:00.0000000 09:03:00.0000000 09:05:00.0000000 08:38:00.0000000 Tue
Jack 08:15:00.0000000 09:03:00.0000000 09:05:00.0000000 08:38:00.0000000 Mon
Joan 08:25:00.0000000 08:35:00.0000000 NULL 09:00:00.0000000 Tue
Joan 08:25:00.0000000 08:35:00.0000000 NULL 09:00:00.0000000 Mon
Joan 08:25:00.0000000 08:35:00.0000000 NULL 09:00:00.0000000 Wed
Joan 08:25:00.0000000 08:35:00.0000000 NULL 09:00:00.0000000 Thu
Ken 08:30:00.0000000 08:45:00.0000000 09:05:00.0000000 08:55:00.0000000 Thu
Ken 08:30:00.0000000 08:45:00.0000000 09:05:00.0000000 08:55:00.0000000 Mon
Ken 08:30:00.0000000 08:45:00.0000000 09:05:00.0000000 08:55:00.0000000 Tue
Ken 08:30:00.0000000 08:45:00.0000000 09:05:00.0000000 08:55:00.0000000 Wed
2 提取有效元素。结果类似下面语句生成的结果
;WITH CTE AS(
SELECT *
FROM #Emp a
FULL JOIN (SELECT 'Mon' AS [WeekDay]
UNION ALL
SELECT 'Tue' AS [WeekDay]
UNION ALL
SELECT 'Wed' AS [WeekDay]
UNION ALL
SELECT 'Thu' AS [WeekDay])b ON 1 = 1)
SELECT Name,[WeekDay],
CASE [WeekDay] WHEN 'Mon' THEN Mon
WHEN 'Tue' THEN Tue
WHEN 'Wed' THEN Wed
WHEN 'Thu' THEN Thu ELSE NULL END AS LoginTime
FROM CTE Name WeekDay LoginTime
-------------------------------------------------- ------- ----------------
Ken Mon 08:30:00.0000000
Joan Mon 08:25:00.0000000
Jack Mon 08:15:00.0000000
Bob Mon 09:30:00.0000000
Ken Tue 08:45:00.0000000
Joan Tue 08:35:00.0000000
Jack Tue 09:03:00.0000000
Bob Tue 08:53:00.0000000
Ken Wed 09:05:00.0000000
Joan Wed NULL
Jack Wed 09:05:00.0000000
Bob Wed 09:01:00.0000000
Ken Thu 08:55:00.0000000
Joan Thu 09:00:00.0000000
Jack Thu 08:38:00.0000000
Bob Thu 08:56:00.0000000
3 将Null值元素去除。这个好理解了，中间有Null值的行去除
;WITH CTE AS(
SELECT *
FROM #Emp a
FULL JOIN (SELECT 'Mon' AS [WeekDay]
UNION ALL
SELECT 'Tue' AS [WeekDay]
UNION ALL
SELECT 'Wed' AS [WeekDay]
UNION ALL
SELECT 'Thu' AS [WeekDay])b ON 1 = 1),
CTE2 AS (SELECT Name,[WeekDay],
CASE [WeekDay] WHEN 'Mon' THEN Mon
WHEN 'Tue' THEN Tue
WHEN 'Wed' THEN Wed
WHEN 'Thu' THEN Thu ELSE NULL END AS LoginTime
FROM CTE )
SELECT *
FROM CTE2
WHERE CTE2.LoginTime IS NOT NULL Name WeekDay LoginTime
-------------------------------------------------- ------- ----------------
Ken Mon 08:30:00.0000000
Joan Mon 08:25:00.0000000
Jack Mon 08:15:00.0000000
Bob Mon 09:30:00.0000000
Ken Tue 08:45:00.0000000
Joan Tue 08:35:00.0000000
Jack Tue 09:03:00.0000000
Bob Tue 08:53:00.0000000
Ken Wed 09:05:00.0000000
Jack Wed 09:05:00.0000000
Bob Wed 09:01:00.0000000
Ken Thu 08:55:00.0000000
Joan Thu 09:00:00.0000000
Jack Thu 08:38:00.0000000
Bob Thu 08:56:00.0000000
好！然后结果有没有和直接Unpivot 一样呢~揍是一样啦~当然罗~中间语句可能不是我演示的那样，我主要是演示中间的虚拟表~
好！周四了~再坚持一天~就又可以星期六上班班啦！