我尝试在test_tbl 中添加一个新列column2并将该列设置为默认值'N/A'而不是 null。声明如下：
if not exists (select 1 from syscolumns where object_name(id) = 'test_tbl' and name = 'column2')
begin
alter table test_tbl add column2 varchar(20) default 'N/A' not null
end
错误是
Could not execute statement.
Column names in each table must be unique. Column name 'column2' in table 'test_tbl' is specified more than once.
Sybase error code=2705
Severity Level=16, State=3, Transaction State=1
Line 4
但是如果我添加一列可以为空。
if not exists (select 1 …