Differences between left join and right join in oracle

In layman's terms:

The number of records connected by A left join B is the same as that of Table.

The number of records connected by A right join B is the same as that of Table B.

A left join B is equivalent to B right join

 

Table:

Field_K, Field_A

1

3 B

4 c

Table B:

Field_K, Field_ B

1 x

2 y

4 z

Select a. Field_K, a. Field_A, B. Field_K, B. Field_ B

From a left join B on a. Field_K = B. Field_K

Field_K Field_A Field_K Field_ B

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

1 a 1 x

3 B NULL

4 c 4 z

Select a. Field_K, a. Field_A, B. Field_K, B. Field_ B

From a right join B on a. Field_K = B. Field_K

Field_K Field_A Field_K Field_ B

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

1 a 1 x

NULL 2 y

4 c 4 z --

For example:

Assume that the data in Table a and table B is like this.

A B

Id name id stock

1 a 1 15

2 B 2 50

3 c

Select * from a inner join B on a. id = B. id

This syntax is an internal connection in the connection query. The result is:

The matching records of the two tables are displayed in the result list.

According to the preceding table, the result is as follows:

A. id name B. id stock

1 a 1 15

2 B 2 50

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

Select * from a, B where a. id = B. id

This syntax is another method of writing internal join, and the execution result is the same as that of inner join.

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

Select * from a left/right join B on a. id = B. id

This is the left Outer Join or right Outer Join in the outer join syntax.

If it is a left outer join, it will display all records in Table,

Select a. *, B. * from a left join B on a. id = B. id

The query result is as follows:

A. id name B. id stock

1 a 1 15

2 B 2 50

3 c null

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

If it is a right outer join, it will display all the records in Table B,

Select a. *, B. * from a right join B on a. id = B. id

The query result is as follows:

A. id name B. id stock

1 a 1 15

2 B 2 50

--

Select a. *, B. * from a left join B on a. k = B. k

Select a. *, B. * from a left outer join B on a. k = B. k

---------- The above two types are the same. left join is short for left outer join.

Select a. *, B. * from a left inner join B on a. k = B. k

No such statement. It is a wrong statement.