sql-server - 添加具有先前选择的默认值的列

Question

我得到的值是这样的:

select myValue from myTable where id=5

我想将 nvarchar 列添加到另一个表，其中默认值将是前一个表。

但我不知道如何存储这个先前的值以在我的添加列脚本中使用它:

IF NOT EXISTS(SELECT * FROM sys.columns WHERE [name] = N'NewColumn' AND [object_id] = OBJECT_ID(N'MySecondTable'))
BEGIN
   ALTER TABLE MySecondTable
   ADD    NewColumn nvarchar(250) NOT NULL DEFAULT 'my previous value'     
END
GO

预先感谢您的帮助!

Answer 1

动态 SQL 来救援:

DECLARE @defval NVARCHAR(500)=LEFT((SELECT myValue FROM myTable where id=5),250);
SET @defval=REPLACE(@defval,N'''',N''''''); -- double single quotes for dynamic SQL statements
DECLARE @stmt NVARCHAR(MAX)=N'
  IF NOT EXISTS(SELECT * FROM sys.columns WHERE [name]=N''NewColumn'' AND [object_id]=OBJECT_ID(N''MySecondTable''))
  BEGIN
    ALTER TABLE MySecondTable
    ADD NewColumn nvarchar(250) NOT NULL DEFAULT N'''+@defval+'''
  END;
';
EXECUTE sp_executesql @stmt;