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, 44 insertions, 0 deletions

diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 8160d78ec6d..79df80704d7 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -4584,6 +4584,50 @@ parse_datetime(text *date_txt, text *fmt, Oid collid, bool strict,
 }
 
 /*
+ * Parses the datetime format string in 'fmt_str' and returns true if it
+ * contains a timezone specifier, false if not.
+ */
+bool
+datetime_format_has_tz(const char *fmt_str)
+{
+	bool		incache;
+	int			fmt_len = strlen(fmt_str);
+	int			result;
+	FormatNode *format;
+
+	if (fmt_len > DCH_CACHE_SIZE)
+	{
+		/*
+		 * Allocate new memory if format picture is bigger than static cache
+		 * and do not use cache (call parser always)
+		 */
+		incache = false;
+
+		format = (FormatNode *) palloc((fmt_len + 1) * sizeof(FormatNode));
+
+		parse_format(format, fmt_str, DCH_keywords,
+					 DCH_suff, DCH_index, DCH_FLAG, NULL);
+	}
+	else
+	{
+		/*
+		 * Use cache buffers
+		 */
+		DCHCacheEntry *ent = DCH_cache_fetch(fmt_str, false);
+
+		incache = true;
+		format = ent->format;
+	}
+
+	result = DCH_datetime_type(format);
+
+	if (!incache)
+		pfree(format);
+
+	return result & DCH_ZONED;
+}
+
+/*
  * do_to_timestamp: shared code for to_timestamp and to_date
  *
  * Parse the 'date_txt' according to 'fmt', return results as a struct pg_tm,