sql as別名使用方法

sql as別名使用方法

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)

把長的語句轉換簡短的語句

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 |
+------------+------------+------------+------------+

在聯合join查詢中經常會用到別名的as 下面看個實例。

mysql> SELECT O.ID from Employee AS O, job AS C
    -> WHERE C.ID = O.ID;