MySQL / vb.NET: Check exisiting data before run the insert query - mysql

Question

I'm using vb.net to create API (MySQL). I know how to run create API for insert, select, and update. Now, I want to create an API that before data insert, must check the data, either exist in the table or not. If exist, then cannot insert the data. Below is my current vb.net code:
<WebMethod()>
<ScriptMethod(ResponseFormat:=ResponseFormat.Json, UseHttpGet:=False, XmlSerializeString:=False)>
Public Sub TGWL_insertLoadingSV(bl_id As String, cont_size_id As String, straping As String)
Dim mySQLConnection As MySqlConnection = New MySqlConnection("Data Source=" & l_DB_SERVER & ";Initial Catalog=" & l_DB_NAME & ";User Id=" & l_DB_USER & ";Password=" & l_DB_PASS)
Dim myDataAdapter As MySqlDataAdapter
Dim myDataset As DataSet = New DataSet
Dim myJson As String = ""
Try
If bl_id.Length > 0 Or cont_size_id.Length > 0 Or straping.Length > 0 Then
Dim myResponse As New failResponceClass
myDataAdapter = New MySqlDataAdapter
myDataAdapter.InsertCommand = New MySqlCommand("BEGIN;
INSERT INTO wla_loading_sv (bl_id, cont_size_id)
VALUES ('" & bl_id & "', '" & cont_size_id & "');
INSERT INTO wla_special_req (bl_id, straping)
VALUES('" & bl_id & "', '" & straping & "');
COMMIT;")
myDataAdapter.InsertCommand.Connection = mySQLConnection
mySQLConnection.Open()
myDataAdapter.InsertCommand.ExecuteNonQuery()
mySQLConnection.Close()
myResponse.statusCode = 1
myResponse.errCode = ""
myResponse.title = l_Title_TGWLAppUser
myResponse.desc = "TGWL App User"
Me.Context.Response.ContentType = "application/json; charset=utf-8"
Me.Context.Response.Write(JsonConvert.SerializeObject(myResponse))
Else
Dim myFailedResponce As New failResponceClass
myFailedResponce.statusCode = 0
myFailedResponce.errCode = "R01"
myFailedResponce.title = l_Title_TGWLAppUser
myFailedResponce.desc = "Missing parmeter."
Me.Context.Response.ContentType = "application/json; charset=utf-8"
Me.Context.Response.Write(JsonConvert.SerializeObject(myFailedResponce))
End If
Catch ex As SoapException
Throw ex
Finally
MySqlConnection.ClearPool(mySQLConnection)
MySqlConnection.ClearAllPools()
mySQLConnection.Close()
mySQLConnection.Dispose()
End Try
End Sub
Thus, how do I want to make sure that the bl_id does not exist at wla_loading_sv table? I want to make it in one API. Can someone help?