Question

I want to know the difference (visually) would be the best between the two following SELECT statements.

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 

and

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

They do not return the same number of rows. Lets say Table1 has 5000 rows and Table2 has 5000 rows also. The first select join statement returns ~40000 rows (specific to my query at work) and then when the where clause is applied, it returns about 2000 rows.

The second select join statement returns 5000 rows (original number). This is the number I want.

But I can’t seem to understand why this is happening. My knowledge and visuallizing joins is a bit weak.

Sample Data: Please change the name of the temp tables, they are the same. Also I couldn’t provide proper column names but have edited my code to indicate which columsn I want match
Here is 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

Here is Table2:
————— #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

Answer 1

If you put filter criteria in the WHERE clause, and that criteria dictates conditions against the “outer” tables of a join, you effectively turn that outer join into an inner join. Filter criteria against an outer join table belongs in the join, not in the where.

How many rows does this version yield?

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';

Theoretically, this should yield >= the number of rows in your first statement, and = the number of rows in your second.

If you want to compare this with your existing result, you can do:

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;

If you get no results, they’re the same. You could also do it the opposite way:

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;

If you get 5000 rows (or whatever the exact row count is for the latter query by itself), then the result sets are the same.