MySQL Learning: Left JOIN, right join, INNER join

Table A is as follows:

AID	Anum
1	a20110111
2	a20110112
3	a20110113
4	a20110114
5	a20110115

Table B is as follows:

BID	Bname
1	bName0111
2	bName0112
3	bName0113
4	bName0114
8	bName0118

One, left join ... on

MySQL statement:

SELECT * from a left JOIN b on a.aid = B.bid

The results are as follows:

AID	Anum	BID	Bname
1	a20110111	1	bName0111
2	a20110112	2	bName0112
3	a20110113	3	bName0113
4	a20110114	4	bName0114
5	a20110115	Null	Null

Description

A LEFT join is based on a record of a table, a can be viewed as the left-hand table, B can be viewed as the right table, and a left table is the Ieft join. In other words, the records in the left table (A) will all be represented, and the right table (B) will only display records for the compound search condition (in the example: A.aid = b.bid).

b tables where the records are insufficient are null.

Second, right join ... on

The MySQL 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	a20110111	1	bName0111
2	a20110112	2	bName0112
3	a20110113	3	bName0113
4	a20110114	4	bName0114
Null	Null	8	bName0118

Description

Right join is the opposite of the result of the left join, this time based on the right-hand table (B), where a table is deficient with null padding.

Third, inner join ... on

The MySQL statement is as follows:

SELECT * from a INNER JOIN b on a.aid = B.bid

Equivalent to:

SELECT * from A, b WHERE a.aid = B.bid

The results are as follows:

AID	Anum	BID	Bname
1	a20110111	1	bName0111
2	a20110112	2	bName0112
3	a20110113	3	bName0113
4	a20110114	4	bName0114

Description

The inner join is not based on who, it just shows the records that qualify.

The left JOIN operation is used in any Frome phrase.