Update multiple rows in bigquery (Google Standard SQL dialect)

I'm running an sql query to update multiple rows at once. The below code works in mysql, but when I run it in bigquery PRIORITY is set to null. What is wrong with my syntax?

UPDATE griffinDataset
    SET PRIORITY = (case when SDC_LOCATIONID = 5920 then 1
                         when SDC_LOCATIONID = 5965 AND DFC_LOCATIONID = 5882 then 2
                         when SDC_LOCATIONID = 5362 AND DFC_LOCATIONID = 5882 then 3
                         when SDC_LOCATIONID = 5852 AND DFC_LOCATIONID = 5882 then 4 
                    end) WHERE 1=1;