mysql 别名

mysql> use zhenyu;
Database changed
mysql> create table `one`(
    -> id int unsigned not null auto_increment primary key,
    -> `username` varchar(50) not null,
    -> `password` varchar(32) not null,
    -> `age` int not null
    -> )engine=myisam default charset=utf8;
Query OK, 0 rows affected (0.00 sec)
 
mysql> select id,username,password,age from  one ;
Empty set (0.00 sec)

mysql> insert into one(id,username,password,age) values('null','zhang1','123','2
0');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> insert into one(id,username,password,age) values('null','zhang2','123','2
1');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> insert into one(id,username,password,age) values('null','zhang3','123','2
2');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> insert into one(id,username,password,age) values('null','zhang3','123','2
3');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> insert into one(id,username,password,age) values('null','zhang5','123','2
4');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> insert into one(id,username,password,age) values('null','zhang6','123','2
6');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> select * from one;
+----+----------+----------+-----+
| id | username | password | age |
+----+----------+----------+-----+
|  1 | zhang1   | 123      |  20 |
|  2 | zhang2   | 123      |  21 |
|  3 | zhang3   | 123      |  22 |
|  4 | zhang3   | 123      |  23 |
|  5 | zhang5   | 123      |  24 |
|  6 | zhang6   | 123      |  26 |
+----+----------+----------+-----+
6 rows in set (0.00 sec)

mysql> select id,username,password,age from one;
+----+----------+----------+-----+
| id | username | password | age |
+----+----------+----------+-----+
|  1 | zhang1   | 123      |  20 |
|  2 | zhang2   | 123      |  21 |
|  3 | zhang3   | 123      |  22 |
|  4 | zhang3   | 123      |  23 |
|  5 | zhang5   | 123      |  24 |
|  6 | zhang6   | 123      |  26 |
+----+----------+----------+-----+
6 rows in set (0.00 sec)

mysql> select o.id,o.username,o.password,o.age from one as o;
+----+----------+----------+-----+
| id | username | password | age |
+----+----------+----------+-----+
|  1 | zhang1   | 123      |  20 |
|  2 | zhang2   | 123      |  21 |
|  3 | zhang3   | 123      |  22 |
|  4 | zhang3   | 123      |  23 |
|  5 | zhang5   | 123      |  24 |
|  6 | zhang6   | 123      |  26 |
+----+----------+----------+-----+
6 rows in set (0.00 sec)

mysql> select one.id,one.username,one.password,one.age from one ;
+----+----------+----------+-----+
| id | username | password | age |
+----+----------+----------+-----+
|  1 | zhang1   | 123      |  20 |
|  2 | zhang2   | 123      |  21 |
|  3 | zhang3   | 123      |  22 |
|  4 | zhang3   | 123      |  23 |
|  5 | zhang5   | 123      |  24 |
|  6 | zhang6   | 123      |  26 |
+----+----------+----------+-----+
6 rows in set (0.00 sec)

mysql> select id,username,password from one;
+----+----------+----------+
| id | username | password |
+----+----------+----------+
|  1 | zhang1   | 123      |
|  2 | zhang2   | 123      |
|  3 | zhang3   | 123      |
|  4 | zhang3   | 123      |
|  5 | zhang5   | 123      |
|  6 | zhang6   | 123      |
+----+----------+----------+
6 rows in set (0.00 sec)

mysql> select id as i,username as u,password as p from one;
+---+--------+-----+
| i | u      | p   |
+---+--------+-----+
| 1 | zhang1 | 123 |
| 2 | zhang2 | 123 |
| 3 | zhang3 | 123 |
| 4 | zhang3 | 123 |
| 5 | zhang5 | 123 |
| 6 | zhang6 | 123 |
+---+--------+-----+
6 rows in set (0.00 sec)
 
mysql> select id as '编号',username as '名字',password as '密码' from one;
+------+--------+------+
| 编号     | 名字       | 密码     |
+------+--------+------+
|    1 | zhang1 | 123  |
|    2 | zhang2 | 123  |
|    3 | zhang3 | 123  |
|    4 | zhang3 | 123  |
|    5 | zhang5 | 123  |
|    6 | zhang6 | 123  |
+------+--------+------+
6 rows in set (0.00 sec)




















select id as 编号, name as 名字, password as 密码 from app01_userinfo;

select id as D, name as N, password as P from app01_userinfo;

select a.id,a.name,a.password from app01_userinfo as a;

select id,name,password from app01_userinfo;

select app01_userinfo.id,app01_userinfo.name,app01_userinfo.password from app01_userinfo;

老哥给我敲的一段 顿时间明白了 

 

其实别名就是一个等量代换的过程 俗语赋值  就是简写                    切记 表名一般为别名 唯独字段不能为别名 

                                              $a = 10;

                                              $b = 10;

                                              $a = $b ;