What is this doing? SELECT (a,b,c) FROM mytable ...

What syntax or operator did I (accidentally) invoke by putting parentheses
around my column list?
     SELECT (a, b, c) FROM mytable...
It gets me a single result column with comma-separated values in
parentheses (see 2nd SELECT below).  I can't find an explanation in the
PostgreSQL manual. It doesn't seem to be an array, a subquery, row
constructor, etc. What sort of thing is it?


test=> CREATE TABLE mytable (a INTEGER, b INTEGER, c INTEGER);
test=> INSERT INTO mytable VALUES (1, 2, 3), (4, 5, 6), (7, 8, 9);
test=> SELECT a, b, c FROM mytable ORDER BY 1;
 a | b | c
---+---+---
 1 | 2 | 3
 4 | 5 | 6
 7 | 8 | 9
(3 rows)

test=> SELECT (a, b, c) FROM mytable ORDER BY 1;
   row
---------
 (1,2,3)
 (4,5,6)
 (7,8,9)
(3 rows)