mysql - 我如何将 "select"用于具有 "not in (a subquery)"的数据表

Question

我想在数据表 dt1 上执行此查询:

select * from dt1 where col1 NOT IN(select col1 from dt2)

测试代码如下:

Sub Main()
    Dim dt1 As New DataTable
    Dim dt2 As New DataTable
    Dim dt3 As New DataTable
    dt1.Columns.Add("col1")
    dt1.Columns.Add("col2")
    dt1.Columns.Add("col3")
    dt1.Rows.Add("1", "a", "a")
    dt1.Rows.Add("2", "b", "b")
    dt1.Rows.Add("3", "c", "c")
    dt1.Rows.Add("4", "d", "d")
    dt1.Rows.Add("5", "e", "e")

    dt2.Columns.Add("col1")
    dt2.Columns.Add("col4")
    dt2.Columns.Add("col5")
    dt2.Rows.Add("1", "a", "a")
    dt2.Rows.Add("2", "f", "f")
    dt2.Rows.Add("3", "g", "g")

    dt3.Columns.Add("col1")
    dt3.Columns.Add("col2")
    dt3.Columns.Add("col3")

    'Dim rows() As DataRow = dt1.Select("dt1.select(columns(0)) Not In (dt2.select(cloumns(0)))")

End Sub

Answer 1

看看Enumerable.Except方法。示例:

dt2.AsEnumerable.Except(dt1.AsEnumerable, DataRowComparer.Default)

根据您认为“不在 Dt2 中”的内容，您可能需要定义自定义 IEqualityComparer .