sql server 的临时表和表变量

临时表

本地临时表

　　适合开销昂贵   结果集是个非常小的集合

-- Local Temporary Tables

IF OBJECT_ID('tempdb.dbo.#MyOrderTotalsByYear') IS NOT NULL
  DROP TABLE dbo.#MyOrderTotalsByYear;
GO

CREATE TABLE #MyOrderTotalsByYear
(
  orderyear INT NOT NULL PRIMARY KEY,
  qty       INT NOT NULL
);

INSERT INTO #MyOrderTotalsByYear(orderyear, qty)
  SELECT
    YEAR(O.orderdate) AS orderyear,
    SUM(OD.qty) AS qty
  FROM Sales.Orders AS O
    JOIN Sales.OrderDetails AS OD
      ON OD.orderid = O.orderid
  GROUP BY YEAR(orderdate);

SELECT Cur.orderyear, Cur.qty AS curyearqty, Prv.qty AS prvyearqty
FROM dbo.#MyOrderTotalsByYear AS Cur
  LEFT OUTER JOIN dbo.#MyOrderTotalsByYear AS Prv
    ON Cur.orderyear = Prv.orderyear + 1;
GO