不是一个实例具有以下工作:C#SQL选择右表在左联接仅返回唯一值,每个
string strSelectSql = "SELECT Table1.ID, Table1.Status,
Table1.CustomerName,Table1.Date, Table1.LocationID,
Table2.LocationID As [LocationID 2] FROM Table1 LEFT JOIN
Table2 ON Table1.ID = Table2.ID
WHERE (Date Is Null AND ID= @SearchForString AND
Status != 'Archived') OR
((Date Between @FromDate AND @ToDate)
AND ID= @SearchForString AND Status != 'Archived')";
SqlConnection SqlConn = new SqlConnection(cstrDatabaseConnection);
SqlDataAdapter SqlAdpt = new SqlDataAdapter();
SqlCommand SqlCom = new SqlCommand(strSelectSql,SqlConn);
SqlCom.Parameters.AddWithValue("@SearchForString",strSearchString);
SqlCom.Parameters.AddWithValue("@FromDate",strFromDate);
SqlCom.Parameters.AddWithValue("@ToDate",strToDate);
SqlAdpt.SelectCommand = SqlCom;
try
{
DataSet TempDS = new DataSet();
SqlConn.Open();
SqlAdpt.Fill(TempDS);
SqlConn.Close();
SqlConn.Dispose();
if (Convert.ToInt32(TempDS.Tables[0].Rows.Count) > 0)
{
dgvQueryResult.DataSource = TempDS.Tables[0];
dgvQueryResult.Refresh();
dgvQueryResult.AutoResizeColumns(DataGridViewAutoSizeColumnsMode.AllCells);
TempDS.Dispose();
}
}
catch (SqlException sqlE)
{
MessageBox.Show(sqlE.Message);
SqlConn.Close();
SqlConn.Dispose();
}
catch (Exception UnknownE)
{
MessageBox.Show(string.Format("Unknown Exception: {0}",UnknownE.Message);
SqlConn.Close();
SqlConn.Dispose();
}
finally
{
if (SqlConn != null) SqlConn.Dispose();
}
现在,这一切工作正常,很正常,除非表2对LocationID
多个值Table2
+----+------------+
| ID | LocationID |
+----+------------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
| 6 | 6 |
| 6 | 7 |
| 6 | 7 |
| 7 | 8 |
| 7 | 9 |
+----+------------+
我想忽略:
Table2
+----+------------+
| ID | LocationID |
+----+------------+
| 6 | 7 |
| 6 | 7 |
+----+------------+
,并得到这个:
Table2
+----+------------+
| ID | LocationID |
+----+------------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
| 6 | 6 |
| 7 | 8 |
| 7 | 9 |
+----+------------+
但我想:
Table2
+----+------------+
| ID | LocationID |
+----+------------+
| 6 | 6 |
+----+------------+
因为LocationID不重复。
另外,我想:
Table2
+----+------------+
| ID | LocationID |
+----+------------+
| 7 | 8 |
| 7 | 9 |
+----+------------+
再次因为LocationID不重复。
如果非要或是否会更有效率我也愿意之前删除从TempDS这些行:
dgvQueryResult.DataSource = TempDS.Tables[0];
如果连必要时,或者最有效的直接从dgvQueryResult
删除条目而不是
首先执行CTE以获取计数大于1的项目,然后将其添加到where子句以排除这些项目。我会给你SQL,但我必须去开会。 – Hogan 2013-03-15 16:14:49
如果您不熟悉如何创建公用表达式(CTE),可以查看此MSDN网站[CTE SQL Server](http://msdn.microsoft.com/zh-cn/library/ms190766(v = sql.105).aspx) – MethodMan 2013-03-15 16:19:50
@Hogan我曾尝试过,但不确定的sytax,因为我在strSelectSql的开头添加了任何形式的WITH我得到了一个SqlException。我以前从来没有使用过CTE或之前有Having Count(*)= 1的函数。而且在这个主题上找不到很多很棒的文档,尤其是在C#中使用它时。 – user2140261 2013-03-15 16:21:29