The difference between the inner join, the left join, and the right join in SQL

Here's a look at the difference between the inner join, the left JOIN, the right Join

Now I'm assuming there's A and B tables.

Left Join

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

At this point on the left of a table as the base table, a table of data are all displayed, B table of data only shows the display of the conditional expression matching on, the right field data is insufficient to fill with null

Right Join

SELECT * from a a right joins b b on a.aid = B.bid;

At this point, the right side of table B is the base table, the data of table B is all displayed, the data of a table only shows the display of the conditional expression according to the on, the left field data is insufficient to fill with null

INNER JOIN

SELECT * from a a inner joins b b on a.aid = B.bid;

When querying using the inner join, only the data that matches the on expression can be displayed, that is, only the data in the two tables is displayed, the data contained in the single table is not displayed, so null is not present in the table queried when using the inner join.