查询仅在日期中选择月份

Question

I have a query that will select all records from my database based on the month. For example, I want to select all records for the month of January. The month() function doesn't work for me. The ComboBox has a value of month name ("January", "February", etc.). I'm using VB 2010 and my database is Microsoft Access.

query = "SELECT empid, empname, department, empdate, timeinam, " & _
        "timeoutam, lateam, timeinpm, timeoutpm, latepm, thw " & _
        "FROM tbldtr where Month(empdate) =" & cmbMonth.Text

Answer 1

Well, supposing that you have your combobox items sorted in a monthly order (Jan, Feb, March...) then you could write your query as

query = "SELECT empid, empname, department, empdate, timeinam, " & _
        "timeoutam,lateam, timeinpm, timeoutpm,latepm,thw " & _
        "FROM tbldtr where Month(empdate) =" & cmbMonth.SelectedIndex + 1

ComboBox.SelectedIndex property is an integer that tells you the index of the current selected item. This property starts at zero, so adding one, matches the number returned by the VBA Month function

Of course, this means that you have somewhere, before this line, a check that informs your user to select something from the combobox and the combobox itself should have DropDownStyle set to ComboBoxStyle.DropDownList to avoid user inputs its own 'month'

WARNING: While, in this context, (converting an integer to a string) there is no much concern about Sql Injection it is better to not indulge in these practices and use always a parameterized query.

Answer 2

Admittedly this is no different than other responses but wanted to express checking the selected index before executing the query along with best to use parameters as shown below. This is OleDb provider, same applies for all managed data providers just change to the correct one eg SQL server use SqlClient etc.

Load ComboBox

cmbMonth.Items.AddRange(
(
    From M In System.Globalization.CultureInfo.CurrentCulture.DateTimeFormat.MonthNames
    Where Not String.IsNullOrEmpty(M)).ToArray
)

Sample to run statement

If cmbMonth.SelectedIndex > -1 Then
    Using cn As New OleDb.OleDbConnection With
        {
            .ConnectionString = "Your connection string"
        }
        Using cmd As New OleDb.OleDbCommand With
            {
                .Connection = cn,
                .CommandText =
                    "SELECT empid, empname, department, empdate, timeinam, timeoutam, lateam, timeinpm, timeoutpm, latepm, thw " &
                    "FROM tbldtr where Month(empdate) = @SelectedMonth"
            }
            cmd.Parameters.Add(New OleDb.OleDbParameter With
                {
                    .ParameterName = "@SelectedMonth",
                    .DbType = DbType.Int32,
                    .Value = cmbMonth.SelectedIndex + 1
                }
            )
            ' continue
        End Using
    End Using
End If

Answer 3

Month() function returns the Month number ,so your where condition fails.

instead use like,

query = "SELECT empid, empname, department, empdate, timeinam, timeoutam,lateam, timeinpm, timeoutpm,latepm,thw FROM tbldtr where datename(month, empdate) =" & cmbMonth.Text

also try to use Like statement rather than equals in where condition,because you may encounter issues with Character casing.more discussion on Like vs (=) .

hope this helps.

hope this helps.

Answer 4

您还可以使用：

"FROM tbldtr where MonthName(Month(empdate)) ='" & cmbMonth.Text & "'"