Re: SQL/JSON path issues/questions

I'm going to push attached 3 patches if no objections.

Regarding 0003-Separate-two-distinctive-json-errors.patch, I think it
requires more thoughts.

RETURN_ERROR(ereport(ERROR,
(errcode(ERRCODE_SINGLETON_JSON_ITEM_REQUIRED),
errmsg("left operand of jsonpath
operator %s is not a single numeric value",
- jspOperationName(jsp->type)))));
+ jspOperationName(jsp->type)),
+ (llen != 1 ?
+ errdetail("It was an array with %d
elements.", llen):
+ errdetail("The only element was not a
numeric.")))));

When we have more than 1 value, it's no exactly array. Jsonpath can
extract values from various parts of json document, which never
constitute and array. Should we say something like "There are %d
values"? Also, probably we should display the type of single element
if it's not numeric. jsonb_path_match() also throws
ERRCODE_SINGLETON_JSON_ITEM_REQUIRED, should we add similar
errdetail() there?

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company