MySQL connection query

Multi-Table query: (data collection in multiple tables into a table)

SELECT user_name as ' nickname ', Gname as ' game name ', score as ' fraction '

From Users,games,scores

WHERE USERS. User_qq=scores. User_qq

and games. Gno=score. GNO

Connection query: internal and external connections

Inner Connection: The two tables connected are equal, if the contents of the two tables do not correspond then do not connect.

Implicit inner joins: Multiple table names appear directly after the from.

Explicit intra-connection: Seclet user_name from TABLE1 [INNER] JOIN TABLE2 on TABLE1. Col=table2. COL (faster than implicit intra-connection execution)

Outer joins: Left Outer and right outer joins (LETF | Right[outer])

The data in the underlying table must appear, and no data in the other table is represented by a null value.

First appears as the left table, and then appears as the right table.

Seclet User_name,gno,score

From the users left JOIN SCORES on USERS. User_qq=scores. USER_QQ and Gno=5

MySQL connection query