"group by ()" cause parsing exception

[xsgao-github]

Describe the bug
Cannot parse this statement select sum(c) from t group by ().

To Reproduce
Steps to reproduce the behavior:

1. net.sf.jsqlparser.parser.CCJSqlParserUtil.parse("select sum(c) from t group by ()")
2. Exception - Caused by: net.sf.jsqlparser.parser.ParseException: Encountered " "(" "( "" at line 1, column 31.

Expected behavior
Not sure if group by () is SQL compliant, but tested on SQL/PostgreSQL, they both support it.

System

• Database you are using - SQL/PostgreSQL
• Java Version - 1.8
• JSqlParser version - 4.0

[manticore-projects]

Greetings.

While "supported by PostgreSQL" is a strong argument for implementing this "feature", I still wonder: Why would anyone want to write code like that? What does the group by() add to the statement? Am I right to assume, PostgreSQL would silently drop it and just executes

select sum(c)
from t

instead? If so, why not write the SQL exactly like this? Is any RDBMS expecying the empty group by () clause?
Please correct me when I am wrong, but I kind of hesitate to spend my time on supporting 'dead code'.

[xsgao-github]

I also mentioned that SQL server also support that. Didn’t test other db.

I don’t know why someone write it in this way, but Tableau does.

[manticore-projects]

H2 supports it too, both as

select id_instrument, count(*)
from cfe.instrument
group by (id_instrument);

as well as

select count(*)
from cfe.instrument
group by ();

So be it.

[manticore-projects]

Can we close this please, it has been solved, tested and merged.