MySQL Multi-table connection

Cartesian product Select * from a a a B; no conditions are required, two tables are multiplied.

Connection type: Cross connection, inner connection, outer connection.

(1) Cross connection, basically is the same as the Cartesian product connection. SELECT * from A Cross join B where .....

(2) Inner connection: Natural connection, equivalent connection, non-equivalent connection.

A. Natural connection: Use the = operator in the join condition to compare the column values of the join column, but delete the duplicate columns in the Join table.

B. Equivalent connection: Do not delete duplicate columns, a INNER join B on a.id=b.id (can also be implicitly A,bwhere a.id=b.id) A, a, a, a, A and B.

C. Non-equivalent connection: Connect two tables with the <,> operator.

(3) Outer connection: Left outer connection, right outer connection, full outer connection.

A. Left outer connection a outer join B on A.id=b.id

B. Right outer connection A left OUTER join B on A.id=b.id

C. Full outer connection A outer JOIN on A.id=b.id

MySQL Multi-table connection