知识在于积累(.NET之路……)

摘要： 有两个表t1和t2，如下所示：表t1:select * from t1表t2:select * from t2如果SQL语句为：select 0 as cid,'未指定' as name UNION ALL select cid,name from t1则得如下数据：如果SQL语句为：select *,'' as col1 from t1select *,'a' as col1 from t1select *,2 as col1 from t1将分别得到如下三种数据： 阅读全文