PostgreSQL Joins

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Joins:

PostgreSQL JOINS are used to retrieve data from multiple tables. A PostgreSQL JOIN is performed whenever two or more tables are joined in a SQL statement.

Types:

1.Basic Join
2.Inner Join
1.Equal Inner Join
2.Non-equal Inner Join
3.Outer Join
1.Left Outer Join
2.Right Outer Join
3.Full Outer Join
4.Cross Join

Examples:

Sample Tables:

 pearl=# select * from muthu;
 id |    dob     |  place
----+------------+---------
  1 | 1992-04-16 | theni
  4 | 1991-07-22 | madurai
  5 | 1991-07-22 | covai
(3 rows)

pearl=# select * from siva;
 id |   name   | age | salary
----+----------+-----+--------
  1 | muthu    |  21 |   2000
  2 | siva     |  26 |   4000
  3 | thanigai |  27 |   5000
(3 rows)

Basic Join:

pearl=# select a.id,a.name,b.dob from siva a,muthu b where a.id=b.id;
 id | name  |    dob   
----+-------+------------
  1 | muthu | 1992-04-16
(1 row)

Inner Join:

Equal Inner Join:

pearl=# select * from siva a inner join muthu b on a.id=b.id;
 id | name  | age | salary | id |    dob     | place
----+-------+-----+--------+----+------------+-------
  1 | muthu |  21 |   2000 |  1 | 1992-04-16 | theni
(1 row)

Non-equal Inner Join:

pearl=# select * from siva a inner join muthu b on a.id!=b.id;
 id |   name   | age | salary | id |    dob     |  place
----+----------+-----+--------+----+------------+---------
  2 | siva     |  26 |   4000 |  1 | 1992-04-16 | theni
  3 | thanigai |  27 |   5000 |  1 | 1992-04-16 | theni
  1 | muthu    |  21 |   2000 |  4 | 1991-07-22 | madurai
  2 | siva     |  26 |   4000 |  4 | 1991-07-22 | madurai
  3 | thanigai |  27 |   5000 |  4 | 1991-07-22 | madurai
  1 | muthu    |  21 |   2000 |  5 | 1991-07-22 | covai
  2 | siva     |  26 |   4000 |  5 | 1991-07-22 | covai
  3 | thanigai |  27 |   5000 |  5 | 1991-07-22 | covai
(8 rows)

Outer Join:

Left Outer Join:

pearl=# select a.name,b.place from siva a left join muthu b on a.id=b.id;
   name   | place
----------+-------
 muthu    | theni
 siva     |
 thanigai |
(3 rows)

Right Outer Join:

pearl=# select a.name,b.place from siva a right join muthu b on a.id=b.id;
 name  |  place
-------+---------
 muthu | theni
       | madurai
       | covai
(3 rows)

Full Outer Join:

pearl=# select a.name,b.place from siva a full join muthu b on a.id=b.id;
   name   |  place
----------+---------
 muthu    | theni
 siva     |
 thanigai |
          | madurai
          | covai
(5 rows)

Cross Join:

pearl=# select a.id,b.id from siva a cross join muthu b;
 id | id
----+----
  1 |  1
  2 |  1
  3 |  1
  1 |  4
  2 |  4
  3 |  4
  1 |  5
  2 |  5
  3 |  5
(9 rows)

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