How do I add a column to a table in SQL Server that doesn't allow nulls?

Question

I have a table that I want to add a bit column, which I wish to default to false for all existing data.

How do I alter my table in such a way that it allows me to specify NOT NULL before I have inserted false for my existing rows?

Should I create it as nullable, do an insert than switch it non-nullable?

Answer 1

You could add the column and provide the default value to be used for all existing rows.

ALTER TABLE foo 
ADD bar bit 
DEFAULT 0 NOT NULL;

Answer 2

ALTER TABLE foo ADD bar bit DEFAULT 0 NOT NULL WITH VALUES;

“with values”子句将默认值指定为现有行。

Answer 3

As an alternative to the answers listed there is another syntax available which may suit some people better, for example if you use tools like 'ReadyRoll'.

ALTER TABLE [dbo].[FOO] ADD BAR bit NOT NULL CONSTRAINT [df_Bar] DEFAULT 0

Check out this SO answer to see why naming your constraints (the df_Bar above) is nice.

Answer 4

ALTER TABLE dbo.MyTable ADD MyColumn bit NOT NULL DEFAULT 0

对于它的价值，您可以启动企业管理器，在UI中进行更改，然后让它生成更改脚本 - 您可以看到它将如何完成这些任务。

Answer 5

I have also done it as you say "create it as nullable, do an insert than switch it non-nullable". I've not had a problem doing it this way.

I've not yet needed to find a better way, however I'm intrigued if there is another way....

Answer 6

我通常将字段创建为可为空，默认为false，在您的情况下更新数据库中的所有字段，然后将其切换为null