Is there any SQL Statement procedure or code for optional requested field value? - sql

Question

I'm a beginner. I created a database in vb.net and I need to build a query, in the SQL Statement - Table Adapter, which returns records even if parameters are NULL in one or more textbox. To be clear, I have several textboxes (related to fields) with which I can filter record results and I want to refine my research as much as I fill textboxes, reverse if I fill just one of them randomly.
Sorry if I confused you, but I guess you get it anyway.

Answer 1

In its simplest form (assuming SQL server param concepts)
-- Define your columns to pull back/display
select t1.column1, t1.column2, t1.column3...
-- Define the table, give it an alias if you're using more than one or it has a silly name
from thetable t1
-- Apply filters
where
-- For each textbox/column search combo, do this...
(column1 = #field1 or #field1 is null)
or -- If the filter is restrictive, use AND here
(column2 = #field2 or #field2 is null)
or -- If the filter is restrictive, use AND here
...

Answer 2

I would dump the table adapter for this requirement.
I am building the sql string using a StringBuilder. StringBuilder objects are mutable, String is not.
To run this Code
1. I assumed Sql Server. If this is not the case change all the data object (Connectio and Command) to the proper provider.
Add your connection string to the constructor of the connection.
Add your table name where it says "YourTable"
I just used TextBox1 etc. as control names. Use your actual control names
Replace Field1, Field2 etc. with your actual column names.
The parameter names (by convention, they start with #) can be anything you want as long as they match the name you add to the Parameters collection.
You will have to check your database for the actual datatypes of the fields. Be sure to convert the TextBox values to the compatible type. TextBox.Text is a string so it will be compatible to .VarChar but note number types or dates.
I added a Debug.Print to check what the Sql string looks like. Be cautious about where I have spaces when building the string. You can see the result in the immediate window (available from Debug menu).
If you don't already have a DataGridView on your form, add one so you can see the reults of your query.
Finally, always use parameters, use Using...End Using blocks, and open your connection at the last minute.
Private Sub RunDynamicQuery()
Dim sb As New StringBuilder
Dim AndNeeded As Boolean
Dim dt As New DataTable
Using cn As New SqlConnection("Your connection string")
Using cmd As New SqlCommand
sb.Append("Select * From YourTable Where ")
If Not String.IsNullOrEmpty(TextBox1.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox1.Text) Then
sb.Append("Field1 = #Field1")
cmd.Parameters.Add("#Field1", SqlDbType.Int).Value = CInt(TextBox1.Text)
AndNeeded = True
End If
If Not String.IsNullOrEmpty(TextBox2.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox2.Text) Then
If AndNeeded Then
sb.Append(" And")
End If
sb.Append(" Field2 = #Field2")
cmd.Parameters.Add("#Field2", SqlDbType.VarChar).Value = TextBox2.Text
AndNeeded = True
End If
If Not String.IsNullOrEmpty(TextBox3.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox3.Text) Then
If AndNeeded Then
sb.Append(" And")
End If
sb.Append(" Field3 = #Field3")
cmd.Parameters.Add("#Field3", SqlDbType.VarChar).Value = TextBox3.Text
AndNeeded = True
End If
sb.Append(";")
cmd.Connection = cn
Debug.Print(sb.ToString)
cmd.CommandText = sb.ToString
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
End Using
DataGridView1.DataSource = dt
End Sub