1、inner join
SELECT <select_list> FROM tableA a INNER JOIN tableB b ON a.key=b.key
2、left join
SELECT <select_list> FROM tableA a LEFT JOIN tableB b ON a.key=b.key
3、right join
SELECT <select_list> FROM tableA a RIGHT JOIN tableB b ON a.key=b.key
4、left join (带条件)
SELECT <select_list> FROM tableA a LEFT JOIN tableB b ON a.key=b.key WHERE b.key IS NULL
5、right join (带条件)
SELECT <select_list> FROM tableA a RIGHT JOIN tableB b ON a.key=b.key WHERE a.key IS NULL
6、full outer join
SELECT <select_list> FROM tableA a FULL OUTER JOIN tableB b ON a.key=b.key7、full outer join（带条件）
SELECT <select_list> FROM tableA a FULL OUTER JOIN tableB b ON a.key=b.key WHERE a.key IS NULL OR b.key IS NULL
