title: add descriptions to fields in BigQuery using SQL
body: <p>I would like to add descriptions to each field in a table. My issue is that we are using dbt and this tool recreates the table each time you run a job causing the descriptions to be deleted if they are there. I am able to control the datatypes casting the fields in the last SELECT statement but I am not sure if I can add the description using SQL.</p>
  <p>I have been googling for a while and I am not able to see whether descriptions can be added using SQL this way.</p>
  <p>I've thought a workaround which would be to create the table and then insert but this in theory is bad practice using dbt.</p>
  <p>Thanks!</p>