mysql substring()函数，字符串分割

mysql> select * from test;
+----+------------+-------+-----------+
| id | name       | score | subject   |
+----+------------+-------+-----------+
|   | xiaoming   |     | shuxue    |
|   | xiaohong   |     | shuxue    |
|   | xiaohong   |     | english   |
|   | xiaohong   |     | physics   |
|   | xiaohong   |     | astronaut |
|   | xiaoming   |     | physics   |
|   | xiaoming   |     | astronaut |
|   | xiaoming   |     | english   |
|   | xiaobai    |     | astronaut |
|  | .2xiaobai |     | english   |
|  | .2xiaobai |     | physics   |
|  | 3xiaobai   |     | shuxue    |
|  | 123xiaohei |     | astronaut |
|  | xiaohei    |     | shuxue    |
|  | xiaohei    |     | physics   |
|  | .12xiaohei |     | english   |
+----+------------+-------+-----------+
 rows in set (0.00 sec)

mysql> select substring(name,,) from test where id=;
+---------------------+
| substring(name,,) |
+---------------------+
| ohong               |
+---------------------+
 row in set (0.00 sec)

mysql> select substring(name,,) from test where id=;
+---------------------+
| substring(name,,) |
+---------------------+
| o                   |
+---------------------+
 row in set (0.00 sec)

mysql> select substring(name,,) from test where id=;
+---------------------+
| substring(name,,) |
+---------------------+
| oh                  |
+---------------------+
 row in set (0.00 sec)

mysql> select substring(name,,) from test where id=;
+---------------------+
| substring(name,,) |
+---------------------+
| xi                  |
+---------------------+
 row in set (0.00 sec)

mysql> select substring(name,,) from test where id=;
+---------------------+
| substring(name,,) |
+---------------------+
|                     |
+---------------------+
 row in set (0.00 sec)