mysql> select * from test; +----+------------+-------+-----------+ | id | name | score | subject | +----+------------+-------+-----------+ | 1 | xiaoming | 89 | shuxue | | 2 | xiaohong | 89 | shuxue | | 3 | xiaohong | 80 | english | | 4 | xiaohong | 80 | physics | | 5 | xiaohong | 80 | astronaut | | 6 | xiaoming | 80 | physics | | 7 | xiaoming | 80 | astronaut | | 8 | xiaoming | 80 | english | | 9 | xiaobai | 80 | astronaut | | 10 | 1.2xiaobai | 80 | english | | 11 | 2.2xiaobai | 80 | physics | | 12 | 3xiaobai | 80 | shuxue | | 13 | 123xiaohei | 80 | astronaut | | 14 | xiaohei | 80 | shuxue | | 15 | xiaohei | 80 | physics | | 16 | .12xiaohei | 80 | english | +----+------------+-------+-----------+ 16 rows in set (0.00 sec) mysql> select * from user; +------+----------+-----------+ | id | name | address | +------+----------+-----------+ | 1 | xiaoming | beijing | | 2 | xiaobai | shandong | | 3 | xiaohong | suzhou | | 4 | xiaohei | changchun | +------+----------+-----------+ 4 rows in set (0.00 sec) mysql> select * from user left join test on user.name=test.name; +------+----------+-----------+------+----------+-------+-----------+ | id | name | address | id | name | score | subject | +------+----------+-----------+------+----------+-------+-----------+ | 1 | xiaoming | beijing | 1 | xiaoming | 89 | shuxue | | 3 | xiaohong | suzhou | 2 | xiaohong | 89 | shuxue | | 3 | xiaohong | suzhou | 3 | xiaohong | 80 | english | | 3 | xiaohong | suzhou | 4 | xiaohong | 80 | physics | | 3 | xiaohong | suzhou | 5 | xiaohong | 80 | astronaut | | 1 | xiaoming | beijing | 6 | xiaoming | 80 | physics | | 1 | xiaoming | beijing | 7 | xiaoming | 80 | astronaut | | 1 | xiaoming | beijing | 8 | xiaoming | 80 | english | | 2 | xiaobai | shandong | 9 | xiaobai | 80 | astronaut | | 4 | xiaohei | changchun | 14 | xiaohei | 80 | shuxue | | 4 | xiaohei | changchun | 15 | xiaohei | 80 | physics | +------+----------+-----------+------+----------+-------+-----------+ 11 rows in set (0.00 sec) mysql> select * from user right join test on user.name=test.name; +------+----------+-----------+----+------------+-------+-----------+ | id | name | address | id | name | score | subject | +------+----------+-----------+----+------------+-------+-----------+ | 1 | xiaoming | beijing | 1 | xiaoming | 89 | shuxue | | 1 | xiaoming | beijing | 6 | xiaoming | 80 | physics | | 1 | xiaoming | beijing | 7 | xiaoming | 80 | astronaut | | 1 | xiaoming | beijing | 8 | xiaoming | 80 | english | | 2 | xiaobai | shandong | 9 | xiaobai | 80 | astronaut | | 3 | xiaohong | suzhou | 2 | xiaohong | 89 | shuxue | | 3 | xiaohong | suzhou | 3 | xiaohong | 80 | english | | 3 | xiaohong | suzhou | 4 | xiaohong | 80 | physics | | 3 | xiaohong | suzhou | 5 | xiaohong | 80 | astronaut | | 4 | xiaohei | changchun | 14 | xiaohei | 80 | shuxue | | 4 | xiaohei | changchun | 15 | xiaohei | 80 | physics | | NULL | NULL | NULL | 10 | 1.2xiaobai | 80 | english | | NULL | NULL | NULL | 11 | 2.2xiaobai | 80 | physics | | NULL | NULL | NULL | 12 | 3xiaobai | 80 | shuxue | | NULL | NULL | NULL | 13 | 123xiaohei | 80 | astronaut | | NULL | NULL | NULL | 16 | .12xiaohei | 80 | english | +------+----------+-----------+----+------------+-------+-----------+ 16 rows in set (0.00 sec)