T-SQL:透视数据（十三）

透视数据实际上就是行状态转为例状态

先加一张测试表

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    ) NOT NULL,
  qty       INT        NOT NULL,
  CONSTRAINT PK_Orders PRIMARY KEY(orderid)
);

INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
VALUES
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , ),
  (, , );

SELECT * FROM dbo.Orders;

把这张表查出来

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

我们将 custid行转换成例

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 还支持一个子句用于 行转列 PIVOT  是以FROM内嵌 表表达式实现的

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  （数据行）  for  要转的列  IN (转那几个数据)