Add SQL/JSON query functions

This introduces the following SQL/JSON functions for querying JSON
data using jsonpath expressions:

JSON_EXISTS(), which can be used to apply a jsonpath expression to a
JSON value to check if it yields any values.

JSON_QUERY(), which can be used to to apply a jsonpath expression to
a JSON value to get a JSON object, an array, or a string.  There are
various options to control whether multi-value result uses array
wrappers and whether the singleton scalar strings are quoted or not.

JSON_VALUE(), which can be used to apply a jsonpath expression to a
JSON value to return a single scalar value, producing an error if it
multiple values are matched.

Both JSON_VALUE() and JSON_QUERY() functions have options for
handling EMPTY and ERROR conditions, which can be used to specify
the behavior when no values are matched and when an error occurs
during jsonpath evaluation, respectively.

Author: Nikita Glukhov <[email protected]>
Author: Teodor Sigaev <[email protected]>
Author: Oleg Bartunov <[email protected]>
Author: Alexander Korotkov <[email protected]>
Author: Andrew Dunstan <[email protected]>
Author: Amit Langote <[email protected]>
Author: Peter Eisentraut <[email protected]>
Author: Jian He <[email protected]>

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, Álvaro Herrera, Jian He, Anton A. Melnikov,
Nikita Malakhov, Peter Eisentraut, Tomas Vondra

Discussion: https://postgr.es/m/[email protected]
Discussion: https://postgr.es/m/[email protected]
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org
Discussion: https://postgr.es/m/CA+HiwqHROpf9e644D8BRqYvaAPmgBZVup-xKMDPk-nd4EpgzHw@mail.gmail.com
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com

1 files changed, 31 insertions, 0 deletions

diff --git a/src/backend/utils/adt/jsonb.c b/src/backend/utils/adt/jsonb.c
index a941654d5a3..e4562b3c6ce 100644
--- a/src/backend/utils/adt/jsonb.c
+++ b/src/backend/utils/adt/jsonb.c
@@ -2158,3 +2158,34 @@ jsonb_float8(PG_FUNCTION_ARGS)
 
 	PG_RETURN_DATUM(retValue);
 }
+
+/*
+ * Convert jsonb to a C-string stripping quotes from scalar strings.
+ */
+char *
+JsonbUnquote(Jsonb *jb)
+{
+	if (JB_ROOT_IS_SCALAR(jb))
+	{
+		JsonbValue	v;
+
+		(void) JsonbExtractScalar(&jb->root, &v);
+
+		if (v.type == jbvString)
+			return pnstrdup(v.val.string.val, v.val.string.len);
+		else if (v.type == jbvBool)
+			return pstrdup(v.val.boolean ? "true" : "false");
+		else if (v.type == jbvNumeric)
+			return DatumGetCString(DirectFunctionCall1(numeric_out,
+													   PointerGetDatum(v.val.numeric)));
+		else if (v.type == jbvNull)
+			return pstrdup("null");
+		else
+		{
+			elog(ERROR, "unrecognized jsonb value type %d", v.type);
+			return NULL;
+		}
+	}
+	else
+		return JsonbToCString(NULL, &jb->root, VARSIZE(jb));
+}