Using scalar-emits UDFs in GROUP_CONCAT crashes instead of giving an exception message

Detail name	Value
Changelog Number	5897
Type	Bug
Status	Resolved
Affected Versions	EXASOL 6.0.0, EXASolution 5.0.0, Exasol 6.1.0, Exasol 6.1.1
Fix Versions	Exasol 6.1.2
Resolution Date	2019-04-29

Background

Aggregate functions can not immediately be applied on expressions that contain an scalar-emits UDF.
A subselect has to be used, like with analytical Functions.

Problem

The aggregate function GROUP_CONCAT is performing this check poorly, resulting in a "connection lost" / "internal server error" exception.

Example

create schema bug;

create python scalar script emit_something() emits (x int) as
def run(ctx):
    emit(1)
/

create python scalar script return_something() returns int as
def run(ctx):
    return 1
/


--works:
select GROUP_CONCAT(x) from (values 1,2,3 as p(x));

-- works:
select GROUP_CONCAT(return_something()) from (values 1,2,3 as p(x));

--gives a slightly confusing exception: "A scalar script can not be used as a set function"
select MAX(emit_something()) from (values 1,2,3 as p(x));

--crashes:
select GROUP_CONCAT(emit_something()) from (values 1,2,3 as p(x));

Fix

A proper "can not be used" exception should be thrown as in the example above.