sql alert 修改表或增加列
sql 的alert命令是用来修改数据表名,增加列,删除列,修改字段数据类型等.好了下面我们来一个个看实例吧.
数据库ALTER TABLE语法
要添加一列在一个表中,使用下列语法:
ALTER TABLE table_name ADD column_name datatype
来看个增加例的实例:
<pre class="brush:php;toolbar:false">ALTER TABLE tname ALTER COLUMN data year
这样给tname表加上了一个列为data 类型的year字段
上面是在表中加列的语法下面我们再来看看删除列吧 DROP COLUMN column_name
ALTER TABLE table_name DROP COLUMN column_name
来看个<strong>删除列</strong>实例.
<pre class="brush:php;toolbar:false">ALTER TABLE Persons DROP COLUMN DateOfBirth
再来修改字段类型:
ALTER COLUMN column_name datatype _id order by w_support desc
P_Id LastName FirstName Address City <br>1 Hansen Ola Timoteivn 10 Sandnes <br>2 Svendson Tove Borgvn 23 Sandnes <br>3 Pettersen Kari Storgt 20 Stavanger
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