The difference between a left join, right join, inner join in SQL Server

Left join returns records that include all the records in the left table and the equivalent of the junction fields in the right table
Right join returns records that include all records in the right table and the junction fields in the left table
INNER JOIN (equivalent join) returns only rows that have the same join field in two tables

Examples are as follows:
--------------------------------------------
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

--------------------------------------------
1.left Join
The SQL statements are 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)
Result Description:
The left join is based on the records of Table A, 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
The SQL statements are 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:
Looking closely, you will find that the result of the left join is exactly the opposite, this time it is based on the right table (B), where a table is not enough to fill with null.
--------------------------------------------
3.inner Join
The SQL statements are 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

Result Description:
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: FROMtable1 left JOIN table2 on table1.field1 compopr table2.field2

Description: table1, the table2 parameter is used to specify the name of the table to combine records with.
Field1, the Field2 parameter specifies the name of the field being joined. And these fields must have the same data type and contain the same type of data, but they do not need to have the same name.
The COMPOPR parameter specifies the relational comparison operator: "=", "<", ">", "<=", ">=", or "<>".
If you are joining a field in a inner JOIN operation that contains data of Memo data type or OLE Object data type, an error occurs.

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

The difference between a left join, right join, inner join in SQL Server