I want to use a workflow to populate a particular field in a list using data drawn from several other fields. I have set up the second part of the workflow with no problem but I need to know if there is a way to get a workflow to check if a field contains existing data. I will then use an IF/Else statement to either use the existing data or fill in the blank field.
You can easily do so in SharePoint Designer workflow and check if the field contains data or not, you can then build a string in the designer calculated from all other fields and set the value for your field with your string. So yes that's doable.