MySQL function, inner join, left outer join, right outer join, cross join difference

Copy it directly, review the knowledge point to see.

1. Inner join: Use the inner join to get the records of the common part of the two tables

2. Outer join: There are two types of outer join, one is Left JOIN and Right JOIN

1）左连接：select * from A Left JOIN B ON A.Aid=B.Bnameid

2）右连接：select * from A Right JOIN B ON A.Aid=B.Bnameid

 

mysql custom function, you can implement custom functions such as count(). Written a bit like a stored procedure.