如何在 MySQL SELECT 中添加一个新列并为其指定一个值?
若要向 MySQL 查询添加列并为其指定一个值,请使用以下语法 −
select yourColumnName1,yourColumnName2,.....N ,yourValue AS anyAliasName from yourTableName;
让我们首先创建一个表 −
mysql> create table DemoTable ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, FirstName varchar(20) ); Query OK, 0 rows affected (0.84 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable(FirstName) values('John'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(FirstName) values('Larry'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable(FirstName) values('Chris'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(FirstName) values('Robert'); Query OK, 1 row affected (0.15 sec)
以下是使用 select 语句从表中显示所有记录的查询 −
mysql> select *from DemoTable;
这将产生以下输出 −
+----+-----------+ | Id | FirstName | +----+-----------+ | 1 | John | | 2 | Larry | | 3 | Chris | | 4 | Robert | +----+-----------+ 4 rows in set (0.00 sec)
以下是向 MySQL 添加一列并为其指定一个值。在创建新列 AGE 之后,我们在其中设置了值 23 −
mysql> select Id,FirstName,23 AS AGE from DemoTable;
这将产生以下输出 −
+----+-----------+-----+ | Id | FirstName | AGE | +----+-----------+-----+ | 1 | John | 23 | | 2 | Larry | 23 | | 3 | Chris | 23 | | 4 | Robert | 23 | +----+-----------+-----+ 4 rows in set (0.00 sec)
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