How does mysql define DISTINCT() in reference documentation

Question

EDIT: This question is about finding definitive reference to MySQL syntax on SELECT modifying keywords and functions. /EDIT

AFAIK SQL defines two uses of DISTINCT k

Answer 1

Interesting scenario.

As you found,

SELECT DISTINCT(a), b, c

is equivalent to:

SELECT DISTINCT (a), b, c

is equivalent to:

SELECT DISTINCT a, b, c

i.e. the parentheses are treated as expression grouping parentheses.

Interestingly, a very similar issue occurs in VB6/VBScript where (for Function(byref x)) Function(x), Function x and Call Function(x) are all slightly different in which value they pass by reference (Function(x) passes a reference to the result of the (x) expression and not x).