Constraints on the SQL Server lookup field

1. When the field does not have a default value or constraint, it can be used:

ALTER TABLE [TABLE_NAME] drop column [column_name] to delete.

When you have a default value, you should first delete the default value and then delete the column, or you will get an error. The specific method is as follows

SelectB.name fromSysobjects bJoinSyscolumns A onb.ID=A.cdefaultwherea.ID= object_id('Table name') andA.name= 'Column Name'”;

ALTER TABLE recording DROP constraint constraint name

ALTER Table table name DROP column name

2. How to add a field in SQL Server

ALTER table name ADD field Name field type default defaults      

Constraints on the SQL Server lookup field