比如:select * from table1,table2 where table1.id = table2.id;
select * from table1 inner join table2 on table1.id = table2.id;
这两个sql语句的区别
select * from table1 left join table2 on table1.id = table2.id;
select * from table1 left outer join table2 on table1.id = table2.id;
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