I want to create a SQL Select Statement but I need to check whether the table in BI Blend exists first.

this should work also!

If (args.FunctionName.XFEqualsIgnoreCase("GetBiBlendTableName"))Then

Dim tableName As String = SharedStringConstants.Unknown
'Get the BI Blend Table Name and throw and error if the table does not exist.
Using dbConnApp As DbConnInfoApp = BRApi.Database.CreateApplicationDbConnInfo(si)
Dim biBlendInfo As StageBiBlendInfo = StageBiBlendInfoCrud.GetInfo(dbConnApp, False, si.WorkflowClusterPk)
tableName = biBlendInfo.BlendTableName
If tableName.XFEqualsIgnoreCase(SharedStringConstants.Unknown) Then
Throw New XFException(si, Nothing, Nothing, "BI-Blend Table Does NOT exist for current Workflow.")
End If
End Using

Return TableName