Ans)
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Sample Img 2
An inner join of TableA and TableB gives the result
of TableA intersect TableB, i.e. the
inner part of a
venn diagram intersection.
An outer join of TableA
and TableB gives the results of TableA union TableB, i.e.
the
outer parts of a venn diagram union.
Examples
Suppose you have two
Tables, with a single column each, and data as follows:
TableA TableB
------ ------
1
3
2
4
3
5
4
6
Note that (1,2) are unique to TableA, (3,4)
are common, and (5,6) are unique to TableB.
Inner
join
An inner join using either of
the equivalent queries gives the intersection of the two
tables,
i.e. the two rows they have in common.
select * from a INNER JOIN b on a.a = b.b;
select a.*,b.* from a,b where a.a = b.b;
TableA | TableB
------ ---+--
3 | 3
4 | 4
Left
outer join
TableA left outer
join will give all rows in TableA, plus any common rows in
TableB.
select * from a LEFT OUTER JOIN b on a.a =
b.b;
select a.*,b.* from a,b where a.a =
b.b(+);
TableA | TableB
-- +-----
1 | null
2 |
null
3
| 3
4
| 4
Full outer
join
TableA full outer join will
give you the union of TableA and TableB, i.e. All the rows
in TableA and all the rows in TableB. If something in TableA
doesn't have a corresponding
data in TableB,
then the TableB portion is null, and vice versa.
select * from TableA FULL OUTER JOIN TableB on a.a = b.b;
TableA |
TableB
----- +-----
1 | null
2 | null
3
| 3
4
| 4
null
| 6
null
| 5
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