T-SQL:透視數據（十三）

透視數據實際上就是行狀態轉為例狀態

先加一張測試表

IF OBJECT_ID('dbo.Orders', 'U') IS NOT NULL DROP TABLE dbo.Orders;
GO

CREATE TABLE dbo.Orders
(
  orderid   INT        NOT NULL,
  orderdate DATE       NOT NULL,
  empid     INT        NOT NULL,
  custid    VARCHAR(5) NOT NULL,
  qty       INT        NOT NULL,
  CONSTRAINT PK_Orders PRIMARY KEY(orderid)
);

INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
VALUES
  (30001, '20070802', 3, 'A', 10),
  (10001, '20071224', 2, 'A', 12),
  (10005, '20071224', 1, 'B', 20),
  (40001, '20080109', 2, 'A', 40),
  (10006, '20080118', 1, 'C', 14),
  (20001, '20080212', 2, 'B', 12),
  (40005, '20090212', 3, 'A', 10),
  (20002, '20090216', 1, 'C', 20),
  (30003, '20090418', 2, 'B', 15),
  (30004, '20070418', 3, 'C', 22),
  (30007, '20090907', 3, 'D', 30);

SELECT * FROM dbo.Orders;

把這張表查出來

SELECT empid, custid, SUM(qty) AS sumqty
FROM dbo.Orders
GROUP BY empid, custid;

我們將 custid行轉換成例 

SELECT empid,
SUM(CASE WHEN custid = 'A' THEN qty END) AS A,
SUM(CASE WHEN custid = 'B' THEN qty END) AS B,
SUM(CASE WHEN custid = 'C' THEN qty END) AS C,
SUM(CASE WHEN custid = 'D' THEN qty END) AS D 
FROM dbo.Orders
GROUP BY empid;

sql server 還支持一個子句用於 行轉列 PIVOT  是以FROM內嵌 表表達式實現的

SELECT empid, A, B, C, D
FROM (SELECT empid, custid, qty
      FROM dbo.Orders) AS D
  PIVOT(SUM(qty) FOR custid IN(A, B, C, D)) AS P;

PIVOT  （數據行）  for  要轉的列  IN (轉那幾個數據)