更改 SQL Server 中的列
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Alter column in SQL Server
提问by GenZiy
What is correct syntax for an ALTERstatement to add a default value to an existing column?
ALTER将默认值添加到现有列的语句的正确语法是什么？
I can add new column with no errors:
我可以添加没有错误的新列：
ALTER TABLE tb_TableName ADD Record_Status varchar(20)
But If I try to alter existing column to apply default value by using the following statement:
但是，如果我尝试使用以下语句更改现有列以应用默认值：
ALTER TABLE tb_TableName
ALTER COLUMN Record_Status VARCHAR(20) NOT NULL DEFAULT ''
or
或者
ALTER TABLE tb_TableName
ALTER Record_Status VARCHAR(20) NOT NULL DEFAULT ''
I have get an error:
我收到一个错误：
Incorrect syntax near 'Record_Status'.
'Record_Status' 附近的语法不正确。
回答by Taryn
I think you want this syntax:
我想你想要这个语法：
ALTER TABLE tb_TableName
add constraint cnt_Record_Status Default '' for Record_Status
Based on some of your comments, I am going to guess that you might already have nullvalues in your table which is causing the alter of the column to not nullto fail. If that is the case, then you should run an UPDATEfirst. Your script will be:
根据您的一些评论，我猜测null您的表中可能已经有值，这会导致更改列not null失败。如果是这种情况，那么您应该先运行UPDATE。您的脚本将是：
update tb_TableName
set Record_Status = ''
where Record_Status is null
ALTER TABLE tb_TableName
ALTER COLUMN Record_Status VARCHAR(20) NOT NULL
ALTER TABLE tb_TableName
ADD CONSTRAINT DEF_Name DEFAULT '' FOR Record_Status
回答by Prakash
Try this one.
试试这个。
ALTER TABLE tb_TableName
ALTER COLUMN Record_Status VARCHAR(20) NOT NULL
ALTER TABLE tb_TableName
ADD CONSTRAINT DEF_Name DEFAULT '' FOR Record_Status
回答by user3262848
To set a default value to a column, try this:
要为列设置默认值，请尝试以下操作：
ALTER TABLE tb_TableName
ALTER COLUMN Record_Status SET DEFAULT 'default value'
