Re: SQL/JSON revisited

On 2023-Apr-04, Amit Langote wrote:

> On Tue, Apr 4, 2023 at 2:16 AM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:

> > - the gram.y solution to the "ON ERROR/ON EMPTY" clauses is quite ugly.
> > I think we could make that stuff use something similar to
> > ConstraintAttributeSpec with an accompanying post-processing function.
> > That would reduce the number of ad-hoc hacks, which seem excessive.
>
> Do you mean the solution involving the JsonBehavior node?

Right. It has spilled as the separate on_behavior struct in the core
parser %union in addition to the raw jsbehavior, which is something
we've gone 30 years without having, and I don't see why we should start
now.

This stuff is terrible:

json_exists_error_clause_opt:
json_exists_error_behavior ON ERROR_P { $$ = $1; }
| /* EMPTY */ { $$ = NULL; }
;

json_exists_error_behavior:
ERROR_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_ERROR, NULL); }
| TRUE_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_TRUE, NULL); }
| FALSE_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_FALSE, NULL); }
| UNKNOWN { $$ = makeJsonBehavior(JSON_BEHAVIOR_UNKNOWN, NULL); }
;

json_value_behavior:
NULL_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_NULL, NULL); }
| ERROR_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_ERROR, NULL); }
| DEFAULT a_expr { $$ = makeJsonBehavior(JSON_BEHAVIOR_DEFAULT, $2); }
;

json_value_on_behavior_clause_opt:
json_value_behavior ON EMPTY_P
{ $$.on_empty = $1; $$.on_error = NULL; }
| json_value_behavior ON EMPTY_P json_value_behavior ON ERROR_P
{ $$.on_empty = $1; $$.on_error = $4; }
| json_value_behavior ON ERROR_P
{ $$.on_empty = NULL; $$.on_error = $1; }
| /* EMPTY */
{ $$.on_empty = NULL; $$.on_error = NULL; }
;

json_query_behavior:
ERROR_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_ERROR, NULL); }
| NULL_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_NULL, NULL); }
| EMPTY_P ARRAY { $$ = makeJsonBehavior(JSON_BEHAVIOR_EMPTY_ARRAY, NULL); }
/* non-standard, for Oracle compatibility only */
| EMPTY_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_EMPTY_ARRAY, NULL); }
| EMPTY_P OBJECT_P { $$ = makeJsonBehavior(JSON_BEHAVIOR_EMPTY_OBJECT, NULL); }
| DEFAULT a_expr { $$ = makeJsonBehavior(JSON_BEHAVIOR_DEFAULT, $2); }
;

json_query_on_behavior_clause_opt:
json_query_behavior ON EMPTY_P
{ $$.on_empty = $1; $$.on_error = NULL; }
| json_query_behavior ON EMPTY_P json_query_behavior ON ERROR_P
{ $$.on_empty = $1; $$.on_error = $4; }
| json_query_behavior ON ERROR_P
{ $$.on_empty = NULL; $$.on_error = $1; }
| /* EMPTY */
{ $$.on_empty = NULL; $$.on_error = NULL; }
;

Surely this can be made cleaner.

By the way -- that comment about clauses being non-standard, can you
spot exactly *which* clauses that comment applies to?

--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
"El número de instalaciones de UNIX se ha elevado a 10,
y se espera que este número aumente" (UPM, 1972)