There are three multi-table query

Multi-table queries in three ways:
 1 Cross query 
syntax: 
the SELECT * from Table 1, Table 2;
 2 in the link query:. Inner join 
an implicit link within the query: do not write the Join keyword Inner 
the SELECT * from the main table, the table on the primary key primary key = from table foreign keys 
displayed in the link to check: write keyword inner join 
the SELECT * from the main table inner join from the table on the primary key primary keys = from the table foreign key.
 3 are linked query. 
left outside link to check the left outer join 
in the left table subject, left table must 
select * from the primary table left outer join from the table on the primary key primary key = the table foreign key 
right outer join query right outer join 
prevail right table, the right and left of the table must 
select * from the primary table from the table on right outer join primary key from the primary key table = outer key