SQL left join and right join)

The following is an example:

Example
Table

Aid adate
1 A1
2 A2
3 A3

Table B

Bid bdate
1 B1
2 B2
4 B4

Left join:

Select * from a left join B on A. Aid = B. Bid

First, retrieve all the data in Table A, and then add the data that matches table A and table B.
In this case, the following information is taken:

1 A1 B1
2 A2 B2
3 A3 null characters

Right join is also available.

This means that all data in Table B is retrieved first, and then the data matching A and B is added.
In this case, the following information is taken:

1 A1 B1
2 A2 B2
4 blank characters B4

Well, you must note that the left and right connections are connected to two tables A and B. The data of fields with the same ID must be retrieved,
Select * from a, B where a. Aid = B. Bid this is to retrieve only matching data.
In this case, the following information is taken:
1 A1 B1
2 A2 B2

By the way, union and Union all

Union is used to connect the data of two tables and exclude all duplicate data.

Union all does not exclude duplicate data.

Below is what you may be interested inArticle:
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