There is an astonishingly large number of (SQL) developers who believe that
DISTINCT is a function that needs parentheses and applies to a single column.
To make this clear
DISTINCT is not a function.
DISTINCT keyword always applies to all columns in the
SELECT list. Enclosing one of the columns in parentheses won’t change anything in the outcome.
The following statements are 100% identical in what they achieve:
SELECT DISTINCT (c1), c2, c3 FROM some_table; SELECT DISTINCT c1, (c2), c3 FROM some_table; SELECT DISTINCT c1, c2, (c3) FROM some_table; SELECT DISTINCT c1, c2, c3 FROM some_table;