A self join is really an inner or outer join on the same table. : Self join « Table Join « SQL Server / T-SQL Tutorial






Selecting books that have the same price.

8>
9> CREATE TABLE titles(
10>    title_id       varchar(20),
11>    title          varchar(80)       NOT NULL,
12>    type           char(12)          NOT NULL,
13>    pub_id         char(4)               NULL,
14>    price          money                 NULL,
15>    advance        money                 NULL,
16>    royalty        int                   NULL,
17>    ytd_sales      int                   NULL,
18>    notes          varchar(200)          NULL,
19>    pubdate        datetime          NOT NULL
20> )
21> GO
1>
2> insert titles values ('1', 'Secrets',   'popular_comp', '1389', $20.00, $8000.00, 10, 4095,'Note 1','06/12/94')
3> insert titles values ('2', 'The',       'business',     '1389', $19.99, $5000.00, 10, 4095,'Note 2','06/12/91')
4> insert titles values ('3', 'Emotional', 'psychology',   '0736', $7.99,  $4000.00, 10, 3336,'Note 3','06/12/91')
5> insert titles values ('4', 'Prolonged', 'psychology',   '0736', $19.99, $2000.00, 10, 4072,'Note 4','06/12/91')
6> insert titles values ('5', 'With',      'business',     '1389', $11.95, $5000.00, 10, 3876,'Note 5','06/09/91')
7> insert titles values ('6', 'Valley',    'mod_cook',     '0877', $19.99, $0.00,    12, 2032,'Note 6','06/09/91')
8> insert titles values ('7', 'Any?',      'trad_cook',    '0877', $14.99, $8000.00, 10, 4095,'Note 7','06/12/91')
9> insert titles values ('8', 'Fifty',     'trad_cook',    '0877', $11.95, $4000.00, 14, 1509,'Note 8','06/12/91')
10> GO

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)

(1 rows affected)
1>
2>      SELECT    DISTINCT t1.price, t1.title
3>      FROM      titles t1
4>                JOIN titles t2 ON t1.price = t2.price
5>                AND t1.title_id <> t2.title_id
6> GO
price                 title
--------------------- --------------------------------------------------------------------------------
              11.9500 Fifty
              19.9900 Prolonged
              19.9900 The
              19.9900 Valley
              11.9500 With

(5 rows affected)
1>
2> drop table titles;
3> GO
1>
2>








4.7.Self join
4.7.1.A self join is really an inner or outer join on the same table.
4.7.2.A self-join that returns Bankers from cities in common with other Bankers
4.7.3.Set join condition in ON clause