mysql> create table student(age int(4), name varchar(20));
Query OK, 0 rows affected (0.09 sec)
mysql> insert into student values(21, 'Jack'), (23, 'Rose'), (35, 'Ann'), (56, 'Mike');
Query OK, 4 rows affected (0.06 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from student;
+------+------+
| age | name |
+------+------+
| 21 | Jack |
| 23 | Rose |
| 35 | Ann |
| 56 | Mike |
+------+------+
4 rows in set (0.00 sec)
（1）为表取别名
mysql> select * from student s where age > 30;
+------+------+
| age | name |
+------+------+
| 35 | Ann |
| 56 | Mike |
+------+------+
2 rows in set (0.00 sec)
mysql>
（2）为字段取别名
mysql> select age as student_age, name as student_name from student;
+-------------+--------------+
| student_age | student_name |
+-------------+--------------+
| 21 | Jack |
| 23 | Rose |
| 35 | Ann |
| 56 | Mike |
+-------------+--------------+
4 rows in set (0.00 sec)
mysql>
