就像Yuck的答案，检查允许脚本运行多次而没有错误。(与使用information_schema.columns相比，代码/自定义字符串更少)

IF object_id('DF_SomeName', 'D') IS NULL BEGIN
    Print 'Creating Constraint DF_SomeName'
   ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn;
END

这将在SQL Server工作:

ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn;

试试下面的命令;

ALTER TABLE Person11
ADD CONSTRAINT col_1_def
DEFAULT 'This is not NULL' FOR Address

就像Yuck的答案，检查允许脚本运行多次而没有错误。(与使用information_schema.columns相比，代码/自定义字符串更少)

IF object_id('DF_SomeName', 'D') IS NULL BEGIN
    Print 'Creating Constraint DF_SomeName'
   ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn;
END

刚刚发现3个简单的步骤来改变已经存在的列，之前是空的

update   orders
set BasicHours=0 where BasicHours is null

alter table orders 
add default(0) for BasicHours

alter table orders 
alter  column CleanBasicHours decimal(7,2) not null 

ALTER TABLE Employee ADD DEFAULT 'SANDNES' FOR CityBorn