sql内联查询

引言

      在项目中一个报表查询功能需要查多张表，用到了内联查询。

      代码如下：

 public DataSet GetConfirmList(FindB_0001InfoEntity entity)
        {
            try
            {
                Database db = DBHelper.CreateDataBase();
                StringBuilder sqlStr = new StringBuilder();
                //报表需要查询内容
                sqlStr.Append("            select * from (");
                sqlStr.Append("         select ROW_NUMBER() OVER(ORDER BY ID desc) AS RowIndex,* from ( ");
                sqlStr.Append("         select B_0001Info.*,A_0004Info.Name as aname,A_0001Info.StateValue as ZhuangTai,A_0009Info.EmployeeName as aen,A_0015Info.DepartmentName as adep from B_0001Info ");
                sqlStr.Append("         inner join A_0004Info on A_0004Info.PlatformID=B_0001Info.PlatformID ");
                sqlStr.Append("         inner join A_0001Info on A_0001Info.StateID=B_0001Info.StateID");
                sqlStr.Append("         inner join A_0009Info on A_0009Info.EmployeeNO=B_0001Info.ApplicantNo");
                sqlStr.Append("         inner join A_0015Info on A_0015Info.DepartmentNo=B_0001Info.Applicantdepartment");
                sqlStr.Append("         where B_0001Info.StateID =6 and B_0001Info.Applicantdepartment='" + entity.DepartmentNO + "' ");
                sqlStr.Append("         and B_0001Info.SubmitTime between '" +entity.BeginDatetime+ "' and '" +entity.EndDatetime+ "' ");
                sqlStr.Append("         ) as b0001) as temp where ");
                sqlStr.Append("         RowIndex>" + entity.StartIndex + " and ");
                sqlStr.Append("         RowIndex<=" + entity.endIndex + " ");

                //查询结果以便分页
                sqlStr.Append("         select count(B_0001Info.ID) from B_0001Info where StateID=6 ");
                sqlStr.Append("         and Applicantdepartment='" + entity.DepartmentNO + "' ");
                sqlStr.Append("         and SubmitTime between '" + entity.BeginDatetime + "' and '" + entity.EndDatetime + "' ");

                
                DbCommand cmd = db.GetSqlStringCommand(sqlStr.ToString());
                DataSet ds = db.ExecuteDataSet(cmd);
                return ds;
            }
            catch (Exception ex)
            {
                log4netHelper.WriteLog(typeof(B_0001InfoDAL), ex);
                return null;
            }
        }

          看起来是不是代码是不是庞多又繁杂。其实原理很简单。

内联查询

         内联查询，联合查询的一种。具体来一个例子你便知道了。

      

select * from Name;

ID Name

1    张三

2    李四

3    王五

select * from Company;

ID Name

1     银行

2     软件

4     房地产

select a.*, b.* from Name as a inner join Company as b on a.ID=b.ID;

ID Name ID Company

1   张三    1   银行

2   李四    2   软件

未完待续

       从上面可以看出，两张表ID一样的都被查询了出来组成一个新表。当然联合查询还有左联，右联，全联。项目中由于sql语句过长，还用到了stringbuilder，它是怎么运用的呢？和stringbuilder和stringbuffer还有string又有什么区别，更多精彩内容下几篇博客继续介绍。