SELECT 的行为变化

Question

我正在将 SQL Server 2008 数据库迁移到 SQL Server 2019，我使用了 Microsoft 数据迁移助手来查找任何行为更改、问题或语法错误。

我有一个 SELECT 给我进行迁移的兼容性错误：

Object uses the old style join syntax which can have poor performance at database compatibility level 90 and higher.

这是我认为错误的 SELECT：

SELECT 
    @Pro = CEILING((BaseDev * 100) / (ISNULL(BaseExe, 0) + ISNULL(BaseDev, 0)))
FROM 
    (SELECT SUM(Base) 'BaseDev'
     FROM Table1
     WHERE Con = @Con AND Lib <> 0 AND Tip = 1 
       AND Fac = 'V' AND ISNULL(Pct, 0) <> 0) A,
    (SELECT SUM(Base) 'BaseExe'
     FROM Table1
     WHERE Con = @Con AND Lib <> 0 AND Tip = 1 AND Fac = 'V' 
       AND ISNULL(Pct, 0) = 0) B

Answer 1

  SELECT @Pro = CEILING((A.BaseDev * 100) / (ISNULL(B.BaseExe, 0) + ISNULL(A.BaseDev, 0)))
   FROM 
   (
       SELECT SUM(Base) AS BaseDev
        FROM Table1
        WHERE Con = @Con AND Lib <> 0 AND Tip = 1 AND Fac = 'V' AND ISNULL(Pct, 0) <> 0
   ) A
  CROSS JOIN 
   (
       SELECT SUM(Base) AS BaseExe
       FROM Table1
       WHERE Con = @Con AND Lib <> 0 AND Tip = 1 AND Fac = 'V' AND ISNULL(Pct, 0) = 0
   ) B

我猜你可以用这个替换你的查询

Answer 2

您可以完全摆脱 JOIN 并使用条件聚合：

WITH CTE AS(
    SELECT SUM(CASE WHEN Pct <> 0 THEN Base END) AS BaseDev,
           SUM(CASE WHEN Pct = 0 OR Pct IS NULL THEN Base END) AS BaseExe
    FROM dbo.Table1
    WHERE Con = @Con
      AND Lib <> 0
      AND Tip = 1
      AND Fac = 'V')
SELECT @Pro = CEILING((BaseDev * 100) / (ISNULL(BaseExe, 0) + ISNULL(BaseDev, 0)))
FROM CTE;

这 也应该 更高效，因为它会导致 table.

的单个 scan/seek

SELECT 的行为变化

Behavior Changes on SELECT

sql

sql-server

migration

compatibility