[英]SQL alter column datatype from nvarchar to int
Can the datatype of a field be changed to int from nvarchar?? 可以将字段的数据类型从nvarchar更改为int吗?
alter table employee alter column designation int
is this valid?? 这有效吗? If not can it be done in some other way?? 如果不能,可以通过其他方式完成吗?
PS: I am using MS SQL Server
PS:我正在使用MS SQL Server
You can try doing an alter table. 您可以尝试做一个变更表。 If it fails do this: 如果失败,请执行以下操作:
ALTER TABLE tableName ADD newCol int;
UPDATE tableName SET newCol = CAST(oldCol AS int)
; UPDATE tableName SET newCol = CAST(oldCol AS int)
;
It is possible only when you column has no value or blank. 仅当您的列没有值或空白时才有可能。 If your column has some value which have nvarchar value and you should try to convert it into int, it will give error. 如果您的列具有一些具有nvarchar值的值,并且您应尝试将其转换为int,它将给出错误信息。
ALTER TABLE [table_name] ALTER COLUMN [column_name] [data_type]
This worked for me (with decimals but I suppose it will work with ints): 这对我有用(带小数点,但我想它将与整数一起工作):
alter table MyTable add MyColNum decimal(15,2) null
go
update MyTable set MyColNum=CONVERT(decimal(15,2), REPLACE(LTRIM(RTRIM(MyOldCol)), ',', '.')) where ISNUMERIC(MyOldCol)=1
go
alter table MyTable drop column MyOldCol
go
EXEC sp_rename 'MyTable.MyColNum', 'MyOldCol', 'COLUMN'
go
Can be done even simpler in just 2 steps 只需2个步骤即可完成
Update the column and set all non numberic values to null so alter won't fail. 更新该列并将所有非数字值设置为null,这样alter不会失败。
Alter the table and set the type to int. 更改表并将类型设置为int。
UPDATE employee
SET designation = (CASE WHEN ISNUMERIC(designation)=1 THEN CAST(CAST(designation AS FLOAT) AS INT)END )
ALTER TABLE employee
ALTER COLUMN designation INT
This takes the assumption that that the columns allow nulls. 假设列允许空值。 If not then that needs to be handled as well. 如果没有,那也需要处理。 For example: By altering the column to allow null, then after it has been converted to int then set all null values to 0 and alter the table to not allow null 例如:通过将列更改为允许null,然后将其转换为int之后,将所有null值设置为0,并将表更改为不允许null
Create a temp column 创建一个临时列
ALTER TABLE MYTABLE ADD MYNEWCOLUMN NUMBER(20,0) NULL;
Copy and casts the data from the old column to the new one 将数据从旧列复制并转换为新列
UPDATE MYTABLE SET MYNEWCOLUMN=CAST(MYOLDCOLUMN AS NUMBER(20,0));
Delete the old column 删除旧列
ALTER TABLE MYTABLE DROP COLUMN MYOLDCOLUMN;
Rename the new one to match the same name as the old one. 重命名新名称,使其与旧名称相同。
ALTER TABLE MYTABLE RENAME COLUMN MYNEWCOLUMN TO MYOLDCOLUMN;
Can you try this ? 你可以试试这个吗?
alter table MyTable add MyColNum Varchar(500) null;
alter table MyTable add MyColNum int null;
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