我想知道两个SELECT语句之间的差异（视觉上）是最好的。
SELECT P.* and X.*
FROM Table1 P
LEFT OUTER JOIN
Table2 X ON
and p.B=x.B
and p.C=x.C
and p.F=x.F
and p.D=x.D
WHERE X.F= 1 and X.E=4
和
SELECT P.* and X.*
FROM Table1 P
LEFT OUTER JOIN
(SELECT * FROM Table2 WHERE X.F= 1 and X.E =4) X
and p.B=x.B
and p.C=x.C
and p.F=x.F
and p.D=x.D
它们不会返回相同数量的行。让我们说Table1有5000行，Table2也有5000行。第一个select join语句返回~40000行（特定于我的工作查询），然后当应用where子句时，它返回大约2000行。
第二个select join语句返回5000行（原始数字）。这是我想要的数字。
但我似乎无法理解为什么会这样。我的知识和可视化连接有点弱。
示例数据：请更改临时表的名称，它们是相同的。此外，我无法提供正确的列名，但已编辑我的代码以指示我想要匹配的columsn 这是TABLE1：
SELECT * INTO #tmp_GridResults_1
FROM (
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'1' AS [E], N'2' AS [F] ) t;
SELECT [ID], [B], [C], [D], [E], [F]
FROM #tmp_GridResults_1
DROP TABLE #tmp_GridResults_1
GO
这是表2： ---------------＃tmp_GridResults_1 ---------------
SELECT * INTO #tmp_GridResults_1
FROM (
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'0' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'0' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'0' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'0' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'0' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'0' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'0' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'0' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'1' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'1' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'2' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'2' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'2' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'2' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'2' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'2' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'2' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'2' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'2' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'2' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'2' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'2' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'3' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'3' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'3' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'3' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'3' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'3' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'3' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'3' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'3' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'3' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'3' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'3' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'4' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'4' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'4' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'4' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'4' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'4' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'4' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'4' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'4' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'4' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'4' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'4' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'98' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'98' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'-1' AS [D], N'98' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'-1' AS [D], N'98' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'98' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'98' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'0' AS [D], N'98' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'0' AS [D], N'98' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'98' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'98' AS [E], N'1' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'1' AS [C], N'1' AS [D], N'98' AS [E], N'2' AS [F] UNION ALL
SELECT N'0' AS [ID], N'P' AS [B], N'2' AS [C], N'1' AS [D], N'98' AS [E], N'2' AS [F] ) t;
SELECT [ID], [B], [C], [D], [E], [F]
FROM #tmp_GridResults_1
DROP TABLE #tmp_GridResults_1
GO
答案 0 :(得分：1)
如果在WHERE子句中放置过滤条件，并且该条件规定了连接的“外部”表的条件，则可以有效地将该外部连接转换为内部连接。针对外连接表的过滤条件属于连接，而不属于where。
此版本产生了多少行？
SELECT P.*, X.*
FROM Table1 P
LEFT OUTER JOIN Table2 X
on P.Id = X.id
and P.name = X.name
and P.age = X.age
AND X.bar = 1
and X.name ='value';
理论上，这应该产生＆gt; =第一个语句中的行数，以及=第二个语句中的行数。
如果您想将此与现有结果进行比较，您可以执行以下操作：
SELECT P.*, X.*
FROM Table1 P
LEFT OUTER JOIN Table2 X
on P.Id = X.id
and P.name = X.name
and P.age = X.age
AND X.bar = 1
and X.name ='value'
EXCEPT
SELECT P.* and X.*
FROM Table1 P
LEFT OUTER JOIN
(SELECT * FROM Table2 WHERE X.bar = 1 and X.name ='value') X
on P.Id = X.id
and P.name = X.name
and P.age = X.age;
如果没有结果，他们就是一样的。您也可以采用相反的方式：
SELECT P.*, X.*
FROM Table1 P
LEFT OUTER JOIN Table2 X
on P.Id = X.id
and P.name = X.name
and P.age = X.age
AND X.bar = 1
and X.name ='value'
INTERSECT
SELECT P.* and X.*
FROM Table1 P
LEFT OUTER JOIN
(SELECT * FROM Table2 WHERE X.bar = 1 and X.name ='value') X
on P.Id = X.id
and P.name = X.name
and P.age = X.age;
如果你得到5000行（或者后者查询本身的确切行数），那么结果集是相同的。