从 dataGridViewComboBoxColumn 中删除重复值

Question

我使用 DataGridViewComboBoxColumn 在 DataGridView 中创建 ComboBox，但我的 ComboBox 不够好。我需要我的 ComboBox 上不包含重复的值。这是一个例子：

苹果
黑莓
Chrome
苹果

我想删除出现多次的值。我怎样才能做到这一点？

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;"

以及如果您希望对其进行排序：

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 unique 语句应用于您的 SQL 之外，在创建第二个表时，还可以对原始 DataTable 应用 unique 语句，如下所示（包含我用于原型设计的单元测试和辅助类）这）。

我在下面添加了一条注释来突出显示应用不同行的行 - 您使用的是 .ToTable() 方法，该方法采用布尔参数 Distinct 来指定仅返回不同行。

[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);
} 

另一种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（尤其是 blob 之类的列），这可能会对性能产生影响，并且还可能意味着您获得的列会破坏查询的独特性质。