hi
based on gram.y and function transformJsonValueExpr.
gram.y:
| JSON_QUERY '('
json_value_expr ',' a_expr json_passing_clause_opt
json_returning_clause_opt
json_wrapper_behavior
json_quotes_clause_opt
json_behavior_clause_opt
')'
| JSON_EXISTS '('
json_value_expr ',' a_expr json_passing_clause_opt
json_on_error_clause_opt
')'
| JSON_VALUE '('
json_value_expr ',' a_expr json_passing_clause_opt
json_returning_clause_opt
json_behavior_clause_opt
')'
json_format_clause_opt contains:
| FORMAT_LA JSON
{
$$ = (Node *) makeJsonFormat(JS_FORMAT_JSON, JS_ENC_DEFAULT, @1);
}
That means, all the context_item can specify "FORMAT JSON" options,
in the meantime, do we need to update these functions
synopsis/signature in the doc?
some examples:
create table a(b jsonb);
create table a1(b int4range);
select json_value(b format json, 'strict $[*]' DEFAULT 9 ON ERROR) from a;
select json_value(b format json, 'strict $[*]' DEFAULT 9 ON ERROR) from a1;
select json_value(text '"1"' format json, 'strict $[*]' DEFAULT 9 ON ERROR);
------------------------------------------------
transformJsonValueExpr
/* Try to coerce to the target type. */
coerced = coerce_to_target_type(pstate, expr, exprtype,
targettype, -1,
COERCION_EXPLICIT,
COERCE_EXPLICIT_CAST,
location);
based on the function transformJsonValueExpr and subfunction
coerce_to_target_type,
for SQL/JSON query functions (JSON_EXISTS, JSON_QUERY, and JSON_VALUE)
the context_item requirement is any data type that not error out while
explicitly casting to jsonb in coerce_to_target_type.
I played around with it, I think these types can be used in context_item.
{char,text,bpchar,character varying } and these types of associated domains.
bytea data type too, but need specify "ENCODING UTF8".
e.g.
select json_value(bytea '"1"' format json ENCODING UTF8, 'strict $[*]'
DEFAULT 9 ON ERROR);
Maybe we can add some brief explanation in this para to explain more
about "context_item"
{
SQL/JSON functions JSON_EXISTS(), JSON_QUERY(), and JSON_VALUE()
described in Table 9.52 can be used to query JSON documents. Each of
these functions apply a path_expression (the query) to a context_item
(the document); see Section 9.16.2 for more details on what
path_expression can contain.
}
