How does Marketing Cloud's SQL in Automation Studio works when having a DISTINCT operator on a data extensions that has a Primary Key (in my case "Customer_Key")? Specifically, does it look for unique primary key values, and ignores the duplicate primary keys form the end-result, or is it looking at the whole data extension for duplicates (i.e. duplicate rows)? If the answer is the latter, how then I can make MC's DISTINCT only apply to primary key?
Here's a simplified extract from my code:
SELECT EmailAddress,First_Name,Last_Name,Address_ID, Customer_Key(PRIMARY KEY) FROM table_1