SQL/JSON query functions

This introduces the SQL/JSON functions for querying JSON data using
jsonpath expressions. The functions are:

JSON_EXISTS()
JSON_QUERY()
JSON_VALUE()

All of these functions only operate on jsonb. The workaround for now is
to cast the argument to jsonb.

JSON_EXISTS() tests if the jsonpath expression applied to the jsonb
value yields any values. JSON_VALUE() must return a single value, and an
error occurs if it tries to return multiple values. JSON_QUERY() must
return a json object or array, and there are various WRAPPER options for
handling scalar or multi-value results. Both these functions have
options for handling EMPTY and ERROR conditions.

Nikita Glukhov

Reviewers have included (in no particular order) Andres Freund, Alexander
Korotkov, Pavel Stehule, Andrew Alsup, Erik Rijkers, Zihong Yu,
Himanshu Upadhyaya, Daniel Gustafsson, Justin Pryzby.

Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru

1 files changed, 47 insertions, 3 deletions

diff --git a/src/backend/utils/adt/jsonfuncs.c b/src/backend/utils/adt/jsonfuncs.c
index a24d498b060..a682d9c9734 100644
--- a/src/backend/utils/adt/jsonfuncs.c
+++ b/src/backend/utils/adt/jsonfuncs.c
@@ -2658,11 +2658,11 @@ populate_array_dim_jsonb(PopulateArrayContext *ctx, /* context */
 
 	check_stack_depth();
 
-	if (jbv->type != jbvBinary || !JsonContainerIsArray(jbc))
+	if (jbv->type != jbvBinary ||
+		!JsonContainerIsArray(jbc) ||
+		JsonContainerIsScalar(jbc))
 		populate_array_report_expected_array(ctx, ndim - 1);
 
-	Assert(!JsonContainerIsScalar(jbc));
-
 	it = JsonbIteratorInit(jbc);
 
 	tok = JsonbIteratorNext(&it, &val, true);
@@ -3134,6 +3134,50 @@ populate_record_field(ColumnIOData *col,
 	}
 }
 
+/* recursively populate specified type from a json/jsonb value */
+Datum
+json_populate_type(Datum json_val, Oid json_type, Oid typid, int32 typmod,
+				   void **cache, MemoryContext mcxt, bool *isnull)
+{
+	JsValue		jsv = { 0 };
+	JsonbValue	jbv;
+
+	jsv.is_json = json_type == JSONOID;
+
+	if (*isnull)
+	{
+		if (jsv.is_json)
+			jsv.val.json.str = NULL;
+		else
+			jsv.val.jsonb = NULL;
+	}
+	else if (jsv.is_json)
+	{
+		text	   *json = DatumGetTextPP(json_val);
+
+		jsv.val.json.str = VARDATA_ANY(json);
+		jsv.val.json.len = VARSIZE_ANY_EXHDR(json);
+		jsv.val.json.type = JSON_TOKEN_INVALID; /* not used in populate_composite() */
+	}
+	else
+	{
+		Jsonb	   *jsonb = DatumGetJsonbP(json_val);
+
+		jsv.val.jsonb = &jbv;
+
+		/* fill binary jsonb value pointing to jb */
+		jbv.type = jbvBinary;
+		jbv.val.binary.data = &jsonb->root;
+		jbv.val.binary.len = VARSIZE(jsonb) - VARHDRSZ;
+	}
+
+	if (!*cache)
+		*cache = MemoryContextAllocZero(mcxt, sizeof(ColumnIOData));
+
+	return populate_record_field(*cache , typid, typmod, NULL, mcxt,
+								 PointerGetDatum(NULL), &jsv, isnull);
+}
+
 static RecordIOData *
 allocate_record_info(MemoryContext mcxt, int ncolumns)
 {