Support parentheses in DISTINCT clause, CURRENT_TIMESTAMP, CURRENT_TIME, and CURRENT_DATE

[yuval-illumex]

The following query works in TrinoDB:

SELECT DISTINCT (orderstatus,orderpriority)
FROM tpch.sf1.orders 
LIMIT 10

[alamb]

Thanks @yuval-illumex -- Sorry for the delay in review

[alamb]

🤔 I didn't catch this prior to merge, but there appears to be a difference between (col1, col2) and col1, col2 in postgres

alamb=# select distinct (t1_id, t1_name) from t1;
  row   
--------
 (11,a)
 (22,b)
 (33,c)
 (44,d)
 (77,e)
(5 rows)

alamb=# select distinct t1_id, t1_name from t1;
 t1_id | t1_name 
-------+---------
    44 | d
    77 | e
    11 | a
    22 | b
    33 | c
(5 rows)

alamb=# 

Turns out mysql doesn't like this syntax at all:

mysql> select distinct t1_id, t1_name from t1;
+-------+---------+
| t1_id | t1_name |
+-------+---------+
|    11 | a       |
|    22 | b       |
|    33 | c       |
|    44 | d       |
|    77 | e       |
+-------+---------+
5 rows in set (0.01 sec)

mysql> select distinct (t1_id, t1_name) from t1;
ERROR 1241 (21000): Operand should contain 1 column(s)
mysql> 

@yuval-illumex any thoughts?