Full SQL join usage

Divided into 1. Inner join 2. Left join 3. Right join 4. left Outer Join

First, set the two tables we want to use.

Table A Table B

ID name ID class

1 IBM 1 C1

2 Sony 3 C3

3 BMW 4 C4

1 inner join: Select * from a inner join B on A. ID = B. ID

Table ID name class

1 IBM C1

3 BMW C3

By the way, the IDs of both tables exist and the combined tables of the two tables are obtained.

2 left join: Select * from a left join B on A. ID = B. ID

Table ID name class

1 IBM C1

2 Sony null

3 BMW C3

The result is that all records of a (table on the left of the Left statement) are obtained, and the records corresponding to table B must be completed if no records exist.

3 right join: Select * from a right join B on A. ID = B. ID

Table ID name class

1 IBM C1

3 BMW C3

4 null C4

Right (right) returns all records of B (table on the right side of the right statement). If the records of Table A do not exist, they must be completed.

4 full outer join: Select * from a full outer join B on A. ID = B. ID

Table ID name class

1 IBM C1

2 Sony null

3 BMW C3

4 null C4