資料結構
計算機網路
關係型資料庫管理系統
作業系統
Java
MS Excel
iOS
HTML
CSS
Android
Python
C 程式設計
C++
C#
MongoDB
MySQL
Javascript
PHP
物理學
化學
生物學
數學
英語
經濟學
心理學
社會學
時尚學
法律學新增查詢中不存在的列？
在查詢中新增不存在的列，可以使用 AS 關鍵字。語法如下 −
SELECT yourColumnName1,yourColumnName2,....N,yourValue AS yourColumnName,....N' FROM yourTableName;
為了理解上述語法，讓我們建立一個表。建立表的查詢如下 −
mysql> create table ColumnDoesNotExists -> ( -> UserId int, -> UserName varchar(20) -> ); Query OK, 0 rows affected (0.67 sec)
示例
使用插入命令在表中插入一些記錄。查詢如下 −
mysql> insert into ColumnDoesNotExists(UserId,UserName) values(100,'Larry'); Query OK, 1 row affected (0.14 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(101,'Sam'); Query OK, 1 row affected (0.22 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(102,'Mike'); Query OK, 1 row affected (0.15 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(103,'David'); Query OK, 1 row affected (0.15 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(104,'Robert'); Query OK, 1 row affected (0.10 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(105,'Maxwell'); Query OK, 1 row affected (0.20 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(106,'Bob'); Query OK, 1 row affected (0.17 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(107,'John'); Query OK, 1 row affected (0.17 sec) mysql> insert into ColumnDoesNotExists(UserId,UserName) values(108,'James'); Query OK, 1 row affected (0.18 sec)
使用 select 語句顯示錶中的所有記錄。查詢如下 −
mysql> select *from ColumnDoesNotExists;
輸出
+--------+----------+ | UserId | UserName | +--------+----------+ | 100 | Larry | | 101 | Sam | | 102 | Mike | | 103 | David | | 104 | Robert | | 105 | Maxwell | | 106 | Bob | | 107 | John | | 108 | James | +--------+----------+ 9 rows in set (0.00 sec)
示例
以下查詢可以新增查詢中不存在的列名 −
mysql> select UserId,UserName,23 AS Age from ColumnDoesNotExists;
輸出
+--------+----------+-----+ | UserId | UserName | Age | +--------+----------+-----+ | 100 | Larry | 23 | | 101 | Sam | 23 | | 102 | Mike | 23 | | 103 | David | 23 | | 104 | Robert | 23 | | 105 | Maxwell | 23 | | 106 | Bob | 23 | | 107 | John | 23 | | 108 | James | 23 | +--------+----------+-----+ 9 rows in set (0.00 sec)
更新於: 26-Jun-2020
1K+ 瀏覽量
廣告