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)
