7种SQL JOIN 关系

# 内连接
select <select_list> from table_a a inner join table_b b on a.key=b.key;

select <select_list> from table_a a right join table_b b on a.key=b.key;

select <select_list> from table_a a left join table_b b on a.key=b.key;

select <select_list> from table_a a left join table_b b on a.key=b.key where b.key is null;

select <select_list> from table_a a right join table_b b on a.key=b.key where a.key is null;

# 全连接
select <select_list> from table_a a full outer join table_b b on a.key=b.key

select <select_list> from table_a a full outer join table_b b on a.key=b.key where a.key is null and b.key is null;