Question

我使用DataGridViewComboBoxColumn在ComboBox中制作DataGridView，但我的ComboBox不够好。我需要我的ComboBox没有重复的值。这是一个例子：

苹果
  黑莓
  铬
   Apple

我想删除多次出现的值。我怎么能这样做？

这是我的代码：

OleDbConnection conn = new OleDbConnection();
OleDbCommand cmd = new OleDbCommand();
Dataset data = new Dataset();
OleDbDataAdapter adapter = new OleDbDataAdapter();
string path = "Data Source = "+".\\"+"test.accdb";
string conStr = "Provider = Microsoft.ACE.OleDb.12.0;"+@path;
conn.Open();
string sql = "SELECT * FROM Table1;"
cmd = new OleDbCommand(sql,conn);
adapter = new OleDbDataAdapter(cmd);
data = new Dataset();
adapter.Fill(data,"Table1");
DataGridViewComboBoxColumn testcolumn = new DataGridViewComboBoxColumn();
testcolumn.Name = "test na ja";
testcolumn.Datasource = data.table[0];
testcolumn.ValueMember = "Remedy";
testcolumn.DisplayMember = "Remedy";
dataGridview1.Columns.Add(testcolumn);
conn.Close()

Answer 1

更改SELECT语句以返回remedy的不同值：

string sql = "SELECT DISTINCT remedy FROM Table1;"

如果您想订购它：

string sql = "SELECT DISTINCT remedy FROM Table1 ORDER BY remedy ASC;"

或

string sql = "SELECT DISTINCT remedy FROM Table1 ORDER BY remedy DESC;"

Answer 2

除了将distinct语句应用于SQL之外，还可以在创建第二个表时对原始DataTable应用distinct，如下所示（包含单元测试和辅助类，我曾用于原型）这一点）。

我在下面添加了一条注释，以突出显示应用了distinct的行 - 您使用的是.ToTable（）方法，它使用布尔参数Distinct指定仅返回不同的行。

[TestMethod]
public void CreateDistinctDataTable()
{
    DataTable originalTable = CreateDataTable();

    AddDataToTable("Fred", "Bloggs", originalTable);
    AddDataToTable("Fred", "Bloggs", originalTable);
    AddDataToTable("John", "Doe", originalTable);

    // This is the key line of code where we use the .ToTable() method
    DataTable distinctTable = originalTable.DefaultView.ToTable( /*distinct*/ true);

    // The original table has two rows with firstname of Fred
    Assert.AreEqual(2, originalTable.Select("firstname = 'Fred'").Length);

    // The new table only has one row with firstname of Fred
    Assert.AreEqual(1, distinctTable.Select("firstname = 'Fred'").Length);
}

private DataTable CreateDataTable()
{
    DataTable myDataTable = new DataTable();

    DataColumn myDataColumn;

    myDataColumn = new DataColumn();
    myDataColumn.DataType = Type.GetType("System.String");
    myDataColumn.ColumnName = "firstname";
    myDataTable.Columns.Add(myDataColumn);

    myDataColumn = new DataColumn();
    myDataColumn.DataType = Type.GetType("System.String");
    myDataColumn.ColumnName = "lastname";
    myDataTable.Columns.Add(myDataColumn);

    return myDataTable;
}

private void AddDataToTable(string firstname,  string lastname, DataTable myTable)
{
    DataRow row = myTable.NewRow();

    row["firstname"] = firstname;            
    row["lastname"] = lastname;

    myTable.Rows.Add(row);
}

另外一个想法是我建议不要在SQL语句中从表中选择*。如果添加更多列（特别是blob），这可能会影响跟踪性能，也可能意味着您会获得打破查询性质的列。

从dataGridViewComboBoxColumn中删除重复的值

2 个答案: