MySQL connection query, encapsulating MySQL function

Connection Query

cross-Connection syntax : SELECT * | Field List from Table 1 Cross Join Table 2

inside　　Connection: Select *| Field list from the left table inner join right table on the left table. field = Right table. field; (inner can be omitted)

Left OUTER join (left connection) Select *| Field list from the left table to the left OUTER join right table on the Open table. field = Right table. field; (outer can be omitted)

Right outer join (right connection)　　　　　select *| Field list from right table left outer join right table. field = left table. field;

Natural Internal Connection Select *| Field left table natural join right table; 　　 The natural inside connection is actually the inner connection, but the condition here is automatically specified by the system

Natural left OUTER join Select *| Field left table natural right table;

Natural right outer join Select *| Field left table natural Right join table;

encapsulate a MySQL function of its own

Application:  

Output Result:

Display in the database:

MySQL connection query, encapsulating MySQL function