Inner join on, the left join on, the difference between right join on and introduction

Table A
Aid Adate
1 A1
2 A2
3 A3
TableB
Bid Bdate
1 B1
2 B2
4 B4
Two tables A, B connected, to remove fields with the same ID
SELECT * from a INNER join B on a.aid = B.bid This is only the matching data is taken out.
At this point, the removal is:
1 A1 B1
2 A2 B2

Then the left join means:
SELECT * from a LEFT join B on a.aid = B.bid
First remove all the data from the a table, and then add the data that matches the A/b
At this point, the removal is:
1 A1 B1
2 A2 B2
3 A3 NULL character

http://hovertree.com/menu/sql/
There's also right join.
Refers to the first to remove all the data in the B table, and then add the data that matches the
At this point, the removal is:
1 A1 B1
2 A2 B2
4 NULL character B4

Left JOIN or left OUTER join.
The result set of the left outer join includes all rows of the left table specified in the OUTER clause.
Instead of just the rows that the join columns match. If a row in the left table does not have a matching row in the right table, all select list columns in the right table in the associated result set row are null values


For example, you'll know!

Table A (A1,B1,C1) b (A2,B2)
A1 B1 C1 A2 B2
01 Mathematics 95 01 Sheets Three
02 Language 90 02 John Doe
03 English 80 04 Harry
Select a.*,b.* from A
INNER join B on (A.A1=B.A2)
The result is:
A1 B1 C1 A2 B2
01 Mathematics 95 01 Sheets Three
02 Language 90 02 John Doe

Select a.*,b.* from A
Left outer join B on (A.A1=B.A2)
The result is:
A1 B1 C1 A2 B2
01 Mathematics 95 01 Sheets Three
02 Language 90 02 John Doe
03 English NULL NULL

Select a.*,b.* from A
Right outer join B on (A.A1=B.A2)
The result is:
A1 B1 C1 A2 B2
01 Mathematics 95 01 Sheets Three
02 Language 90 02 John Doe
Null NULL NULL 04 Harry

Select a.*,b.* from A
Full outer join B on (A.A1=B.A2)
The result is:
A1 B1 C1 A2 B2
01 Mathematics 95 01 Sheets Three
02 Language 90 02 John Doe
03 English NULL NULL
Null NULL NULL 04 Harry

Recommendation: http://www.cnblogs.com/roucheng/p/3504463.html

Inner join on, the left join on, the difference between right join on and introduction