主题：请教一句sql代码

Dim cmd As New SQLCommand
Dim dt As DataTable
Dim cmb As WinForm.ComboBox
cmd.CommandText = "SELECT DISTINCT month(日期) as 月份 From {主表} "
dt = cmd.ExecuteReader()
cmb = e.Form.Controls("月份")
cmb.ComboList= dt.GetComboListString("月份")

这句代码可以通过后台取值，取到所有加载和未加载的"月份"的值

现在想实现：年份的组合框选定了年份后，在选月份的值时，能只加载年份组合框里选定的年份所对应的月份的值

我把sql代码改为： SELECT DISTINCT month(日期) as 月份 From {主表} where year(日期) = nf.text