sql as别名使用方法
mysql教程> CREATE TABLE Topic(
-> TopicID SMALLINT NOT NULL AUTO_INCREMENT
PRIMARY KEY,
-> Name VARCHAR(50) NOT NULL,
-> InStock SMALLINT UNSIGNED NOT NULL,
-> OnOrder SMALLINT UNSIGNED NOT NULL,
-> Reserved SMALLINT UNSIGNED NOT NULL,
-> Department ENUM('Classical', 'Popular') NOT
NULL,
-> Category VARCHAR(20) NOT NULL,
-> RowUpdate TIMESTAMP NOT NULL
-> );
Query OK, 0 rows affected (0.02 sec)
mysql>
mysql>
mysql> INSERT INTO Topic (Name, InStock, OnOrder,
Reserved, Department, Category) VALUES
-> ('Java', 10, 5,
3, 'Popular', 'Rock'),
-> ('JavaScript', 10, 5,
3, 'Classical', 'Opera'),
-> ('C Sharp', 17, 4,
1, 'Popular', 'Jazz'),
-> ('C', 9, 4,
2, 'Classical', 'Dance'),
-> ('C++', 24, 2,
5, 'Classical', 'General'),
-> ('Perl', 16, 6,
8, 'Classical', 'Vocal'),
-> ('Python', 2, 25,
6, 'Popular', 'Blues'),
-> ('Php', 32, 3,
10, 'Popular', 'Jazz'),
-> ('ASP.net', 12, 15,
13, 'Popular', 'Country'),
-> ('VB.net', 5, 20,
10, 'Popular', 'New Age'),
-> ('VC.net', 24, 11,
14, 'Popular', 'New Age'),
-> ('UML', 42, 17,
17, 'Classical', 'General'),
-> ('www.java2s.com',25, 44,
28, 'Classical', 'Dance'),
-> ('Oracle', 32, 15,
12, 'Classical', 'General'),
-> ('Pl/SQL', 20, 10,
5, 'Classical', 'Opera'),
-> ('Sql Server', 23, 12,
8, 'Classical', 'General');
Query OK, 16 rows affected (0.00 sec)
Records: 16 Duplicates: 0 Warnings: 0
mysql>
mysql> select * from Topic;
+---------+----------------+---------+---------+---------
-+------------+----------+---------------------+
| TopicID | Name | InStock | OnOrder | Reserved
| Department | Category | RowUpdate |
+---------+----------------+---------+---------+---------
-+------------+----------+---------------------+
| 1 | Java | 10 | 5 | 3
| Popular | Rock | 2007-07-23 19:09:48 |
| 2 | JavaScript | 10 | 5 | 3
| Classical | Opera | 2007-07-23 19:09:48 |
| 3 | C Sharp | 17 | 4 | 1
| Popular | Jazz | 2007-07-23 19:09:48 |
| 4 | C | 9 | 4 | 2
| Classical | Dance | 2007-07-23 19:09:48 |
| 5 | C++ | 24 | 2 | 5
| Classical | General | 2007-07-23 19:09:48 |
| 6 | Perl | 16 | 6 | 8
| Classical | Vocal | 2007-07-23 19:09:48 |
| 7 | Python | 2 | 25 | 6
| Popular | Blues | 2007-07-23 19:09:48 |
| 8 | Php | 32 | 3 | 10
| Popular | Jazz | 2007-07-23 19:09:48 |
| 9 | ASP.net | 12 | 15 | 13
| Popular | Country | 2007-07-23 19:09:48 |
| 10 | VB.net | 5 | 20 | 10
| Popular | New Age | 2007-07-23 19:09:48 |
| 11 | VC.net | 24 | 11 | 14
| Popular | New Age | 2007-07-23 19:09:48 |
| 12 | UML | 42 | 17 | 17
| Classical | General | 2007-07-23 19:09:48 |
| 13 | www.java2s.com | 25 | 44 | 28
| Classical | Dance | 2007-07-23 19:09:48 |
| 14 | Oracle | 32 | 15 | 12
| Classical | General | 2007-07-23 19:09:48 |
| 15 | Pl/SQL | 20 | 10 | 5
| Classical | Opera | 2007-07-23 19:09:48 |
| 16 | Sql Server | 23 | 12 | 8
| Classical | General | 2007-07-23 19:09:48 |
+---------+----------------+---------+---------+---------
-+------------+----------+---------------------+
16 rows in set (0.00 sec)
mysql>
mysql> SELECT Name, InStock+OnOrder-Reserved AS Available
-> FROM Topic
-> WHERE Name LIKE '%bach%'
-> ORDER BY Name;
Empty set (0.00 sec)
把长的语句转换简短的语句
mysql> SELECT first_name, start_date, CURDATE(),
-> (YEAR(CURDATE())-YEAR(start_date)) - (RIGHT
(CURDATE(),5)<RIGHT(start_date,5))
-> AS YearServed
-> FROM employee ORDER BY YearServed;
+------------+------------+------------+------------+
| first_name | start_date | CURDATE() | YearServed |
+------------+------------+------------+------------+
| Jason | 1996-07-25 | 2007-07-22 | 10 |
| James | 1996-09-17 | 2007-07-22 | 10 |
| David | 1990-12-31 | 2007-07-22 | 16 |
| Linda | 1987-07-30 | 2007-07-22 | 19 |
| Robert | 1984-01-15 | 2007-07-22 | 23 |
| Celia | 1982-10-24 | 2007-07-22 | 24 |
| James | 1978-12-12 | 2007-07-22 | 28 |
| Alison | 1976-03-21 | 2007-07-22 | 31 |
+------------+------------+------------+------------+
在联合join查询中经常会用到别名的as 下面看个实例。
mysql> SELECT O.ID from Employee AS O, job AS C
-> WHERE C.ID = O.ID;
