vb.net使用vb.net更新查询

Question

in an sql updatate query runnging in a vb.net application i am updating the data of some columns to the sql datatable, here is the code

dim cnn = New SqlConnection(connetionString)
Dim q As New SqlCommand("UPDATE products SET rank=@rank,rankchange=@rankchange,PD=@PD,PDP=@PDP,TPD=@TPD where catalogid=@catalogid",cnn)
cnn.Open()
For i = 0 To mainDatatable.Rows.Count - 1
 q.Parameters.Add(New SqlParameter("@rank", mainDatatable.Rows(i)("rank")))
 q.Parameters.Add(New SqlParameter("@rankchange", mainDatatable.Rows(i)("rankchange")))
 q.Parameters.Add(New SqlParameter("@PD", mainDatatable.Rows(i)("PD")))
 q.Parameters.Add(New SqlParameter("@PDP", mainDatatable.Rows(i)("PDP")))
 q.Parameters.Add(New SqlParameter("@TPD", mainDatatable.Rows(i)("TPD")))
 q.ExecuteNonQuery()
 q.Parameters.Clear()
Next

i am having 2 problems

1. its running slow considering that the table has about 60k records
2. if the a value in my datatable application was NULL then i want to update it as NULL, what would be the best way? i tried something like the following

If IsDBNull(mainDatatable.Rows(i)("rank")) Then q.Parameters.Add(New SqlParameter("@rank", "NULL")) Else q.Parameters.Add(New SqlParameter("@rank", mainDatatable.Rows(i)("rank"))) End If

Answer 1

To respond to (1) the speed question...

if you do indeed have 60K+ changes to process you don't need to execute 60K update statements. I would upload the 60K records to a temp table and invoke a stored procedure to do an UPDATE FROM...INNER JOIN statement between the real table and the temp table. Another possible idea if you don't want to rewrite what you've got is to filter out any rows in your datatable that have not been tainted. If there is no change then there is no reason to send those update statements...

Regarding (2) here is syntax...

this should work for you regarding sending NULL values as SqlParameters.

If mainDatatable.Rows(i)("rank") = DBNull.Value Then
  q.Parameters.Add(New SqlParameter("@rankchange", SqlDbType.Int, 4) With { .Value = DBNull.Value })
Else
  q.Parameters.Add(New SqlParameter("@rankchange", SqlDbType.Int, 4) With { .Value = mainDatatable.Rows(i)("rank") })
End If

Answer 2

writing following line of code q.Parameters.Add(New SqlParameter("@rank", "NULL")) doesn't make null entry instead it will treat Null as string.
what you can try is this.

q.Parameters.Add(new SqlParameter() { 
        ParameterName="@test",
        IsNullable=true,
        Value=DBNull.Value
    });