SQL/JSON: add standard JSON constructor functions

This commit introduces the SQL/JSON standard-conforming constructors for
JSON types:

JSON_ARRAY()
JSON_ARRAYAGG()
JSON_OBJECT()
JSON_OBJECTAGG()

Most of the functionality was already present in PostgreSQL-specific
functions, but these include some new functionality such as the ability
to skip or include NULL values, and to allow duplicate keys or throw
error when they are found, as well as the standard specified syntax to
specify output type and format.

Author: Nikita Glukhov <n.gluhov@postgrespro.ru>
Author: Teodor Sigaev <teodor@sigaev.ru>
Author: Oleg Bartunov <obartunov@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Amit Langote <amitlangote09@gmail.com>

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/CAF4Au4w2x-5LTnN_bxky-mq4=WOqsGsxSpENCzHRAzSnEd8+WQ@mail.gmail.com
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Discussion: https://postgr.es/m/20220616233130.rparivafipt6doj3@alap3.anarazel.de
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org

1 files changed, 44 insertions, 0 deletions

diff --git a/src/interfaces/ecpg/test/sql/sqljson.pgc b/src/interfaces/ecpg/test/sql/sqljson.pgc
new file mode 100644
index 00000000000..6a582b5b105
--- /dev/null
+++ b/src/interfaces/ecpg/test/sql/sqljson.pgc
@@ -0,0 +1,44 @@
+#include <stdio.h>
+
+EXEC SQL INCLUDE sqlca;
+exec sql include ../regression;
+
+EXEC SQL WHENEVER SQLERROR sqlprint;
+
+int
+main ()
+{
+EXEC SQL BEGIN DECLARE SECTION;
+  char json[1024];
+EXEC SQL END DECLARE SECTION;
+
+  ECPGdebug (1, stderr);
+
+  EXEC SQL CONNECT TO REGRESSDB1;
+  EXEC SQL SET AUTOCOMMIT = ON;
+
+  EXEC SQL SELECT JSON_OBJECT(RETURNING text) INTO :json;
+  printf("Found json=%s\n", json);
+
+  EXEC SQL SELECT JSON_OBJECT(RETURNING text FORMAT JSON) INTO :json;
+  printf("Found json=%s\n", json);
+
+  EXEC SQL SELECT JSON_ARRAY(RETURNING jsonb) INTO :json;
+  printf("Found json=%s\n", json);
+
+  EXEC SQL SELECT JSON_ARRAY(RETURNING jsonb FORMAT JSON) INTO :json;
+  printf("Found json=%s\n", json);
+
+  EXEC SQL SELECT JSON_OBJECT(1: 1, '1': NULL WITH UNIQUE) INTO :json;
+  // error
+
+  EXEC SQL SELECT JSON_OBJECT(1: 1, '2': NULL, 1: '2' ABSENT ON NULL WITHOUT UNIQUE KEYS) INTO :json;
+  printf("Found json=%s\n", json);
+
+  EXEC SQL SELECT JSON_OBJECT(1: 1, '2': NULL ABSENT ON NULL WITHOUT UNIQUE RETURNING jsonb) INTO :json;
+  printf("Found json=%s\n", json);
+
+  EXEC SQL DISCONNECT;
+
+  return 0;
+}