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 substring(name,4,7) from test where id=3; +---------------------+ | substring(name,4,7) | +---------------------+ | ohong | +---------------------+ 1 row in set (0.00 sec) mysql> select substring(name,4,1) from test where id=3; +---------------------+ | substring(name,4,1) | +---------------------+ | o | +---------------------+ 1 row in set (0.00 sec) mysql> select substring(name,4,2) from test where id=3; +---------------------+ | substring(name,4,2) | +---------------------+ | oh | +---------------------+ 1 row in set (0.00 sec) mysql> select substring(name,1,2) from test where id=3; +---------------------+ | substring(name,1,2) | +---------------------+ | xi | +---------------------+ 1 row in set (0.00 sec) mysql> select substring(name,0,5) from test where id=3; +---------------------+ | substring(name,0,5) | +---------------------+ | | +---------------------+ 1 row in set (0.00 sec)