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Database Outer Join VS Inner Join

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Q)  Database Outer Join VS Inner Join


  • Database Outer Join VS Inner Join
    Sample Img 2

Ans)

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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Database Outer Join VS Inner Join


Database Outer Join VS Inner Join

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