The difference between the left join of SQL, right join, INNER join

Table A records the following:

AID Anum
1 a20050111
2 a20050112
3 a20050113
4 a20050114
5 a20050115

Table B records the following:

BID bname
1 2006032401
2 2006032402
3 2006032403
4 2006032404
8 2006032408

----------------------------------------

The 1.LEFT join SQL statement is as follows: SELECT * from A LEFT join B on a.aid = B.bid

The results are as follows:

AID Anum BID bname
1 a20050111 1 2006032401
2 a20050112 2 2006032402
3 a20050113 3 2006032403
4 a20050114 4 2006032404
5 a20050115 NULL NULL

(The number of rows affected is 5 rows) The result shows that the left join is based on the records of a table, a can be regarded as the right table, and B can be regarded as left table. In other words, the records of the left table (A) will all be represented, and the right table (B) will only display records that match the search criteria (in the example: A.aid = b.bid). The low-record of table B is null. --------------------------------------------2.right Join SQL statement is as follows: SELECT * from A right join B on a.aid = B.bid

The results are as follows:

AID Anum BID bname
1 a20050111 1 2006032401
2 a20050112 2 2006032402
3 a20050113 3 2006032403
4 a20050114 4 2006032404
NULL NULL 8 2006032408

(The number of rows affected is 5 rows) result Description: Look closely, you will find that the result of the left join is exactly the opposite, this time is based on the right table (B), a table is not sufficient place with null padding. --------------------------------------------3.inner Join SQL statement is as follows: SELECT * from A innerjoin B on a.aid = B.bid

The results are as follows:

AID Anum BID bname
1 a20050111 1 2006032401
2 a20050112 2 2006032402
3 a20050113 3 2006032403
4 a20050114 4 2006032404

The result: Obviously, this shows only the records of A.aid = B.bid. This shows that inner join is not based on who, it only shows records that match the criteria. --------------------------------------------Note: The LEFT JOIN operation is used to combine records from the source table in any from clause. Use the left JOIN operation to create an outer join of the side. The left outer join will contain all of the records from the first (left) two tables, even if there are no records of the corresponding values in the second (right) table.

Syntax: from table1 left JOIN table2 on table1.field1 compopr table2.field2

Source: http://www.cnblogs.com/pcjim/articles/799302.html

The difference between the left join of SQL, right join, INNER join