如下两张表：
表A 表B
F F
A A
B B
C F
D G
E H
WHERE:
SELECT A.F AS FA, dbo.B.F AS FB
FROM dbo.A LEFT OUTER JOIN dbo.B ON dbo.A.F = dbo.B.F
WHERE A.F = ' A '
FA FB
A A
AND:
SELECT A.F AS FA, dbo.B.F AS FB
FROM dbo.A LEFT OUTER JOIN dbo.B ON dbo.A.F = dbo.B.F
AND A.F = ' A '
FA FB
A A
B null
C null
D null
E null
可以看出使用 WHERE 条件会筛选连接查询的结果，但不影响返回的右表字段值；
使用 AND 不会对结果进行筛选，结果一定是包含了所有的左表记录，但是会影响
返回的右表字段值，如果 ON 后面的逻辑判断返回 true 显示右表值，为 false 则显示 null。
SELECT A.F AS FA, dbo.B.F AS FB
FROM dbo.A LEFT OUTER JOIN dbo.B ON dbo.A.F = dbo.B.F AND 1 = 1
FA FB
A A
B B
C null
D null
E null
SELECT A.F AS FA, dbo.B.F AS FB
FROM dbo.A LEFT OUTER JOIN dbo.B ON dbo.A.F = dbo.B.F AND 1 = 2
FA FB
A null
B null
C null
D null
E null
如果是 INNER JOIN， WHERE 和 AND 效果相同。
SELECT A.F AS FA, dbo.B.F AS FB
FROM dbo.A INNER JOIN dbo.B ON dbo.A.F = dbo.B.F
WHERE A.F = ' A ' / AND A.F = ' A '
