Re: SQL/JSON revisited - Mailing list pgsql-hackers

On 2023-Apr-04, Amit Langote wrote:

> On Tue, Apr 4, 2023 at 2:16 AM Alvaro Herrera <alvherre@alvh.no-ip.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)