Improve documentation and testing of jsonpath string() for datetimes.

Point out that the output format depends on DateStyle, and test that,
along with testing some cases previously not covered.

In passing, adjust the horology test to verify that the prevailing
DateStyle is 'Postgres, MDY', much as it has long verified the
prevailing TimeZone.  We expect pg_regress to have set these up,
and there are multiple regression tests relying on these settings.

Also make the formatting of entries in table 9.50 more consistent.

David Wheeler (marginal additional hacking by me); review by jian he

Discussion: https://postgr.es/m/56955B33-6959-4FDA-A459-F00363ECDFEE@justatheory.com

doc/src/sgml/func.sgml

@@ -18016,7 +18016,9 @@ ERROR:  jsonpath member accessor can only be applied to an object
         <returnvalue><replaceable>string</replaceable></returnvalue>
        </para>
        <para>
-        String value converted from a JSON boolean, number, string, or datetime
+        String value converted from a JSON boolean, number, string, or
+        datetime (the output format for datetimes is determined by
+        the <xref linkend="guc-datestyle"/> parameter)
        </para>
        <para>
         <literal>jsonb_path_query_array('[1.23, "xyz", false]', '$[*].string()')</literal>
@@ -18105,7 +18107,9 @@ ERROR:  jsonpath member accessor can only be applied to an object
         <returnvalue><replaceable>decimal</replaceable></returnvalue>
        </para>
        <para>
-        Rounded decimal value converted from a JSON number or string. <literal>precision</literal> and <literal>scale</literal> must be integer values.
+        Rounded decimal value converted from a JSON number or string
+        (<literal>precision</literal> and <literal>scale</literal> must be
+        integer values)
        </para>
        <para>
         <literal>jsonb_path_query('1234.5678', '$.decimal(6, 2)')</literal>
@@ -18207,7 +18211,7 @@ ERROR:  jsonpath member accessor can only be applied to an object
        </para>
        <para>
         Time without time zone value converted from a string, with fractional
-        seconds adjusted to the given precision.
+        seconds adjusted to the given precision
        </para>
        <para>
         <literal>jsonb_path_query('"12:34:56.789"', '$.time(2)')</literal>
@@ -18236,7 +18240,7 @@ ERROR:  jsonpath member accessor can only be applied to an object
        </para>
        <para>
         Time with time zone value converted from a string, with fractional
-        seconds adjusted to the given precision.
+        seconds adjusted to the given precision
        </para>
        <para>
         <literal>jsonb_path_query('"12:34:56.789 +05:30"', '$.time_tz(2)')</literal>
@@ -18265,7 +18269,7 @@ ERROR:  jsonpath member accessor can only be applied to an object
        </para>
        <para>
         Timestamp without time zone value converted from a string, with
-        fractional seconds adjusted to the given precision.
+        fractional seconds adjusted to the given precision
        </para>
        <para>
         <literal>jsonb_path_query('"2023-08-15 12:34:56.789"', '$.timestamp(2)')</literal>
@@ -18294,7 +18298,7 @@ ERROR:  jsonpath member accessor can only be applied to an object
        </para>
        <para>
         Timestamp with time zone value converted from a string, with fractional
-        seconds adjusted to the given precision.
+        seconds adjusted to the given precision
        </para>
        <para>
         <literal>jsonb_path_query('"2023-08-15 12:34:56.789 +05:30"', '$.timestamp_tz(2)')</literal>

src/test/regress/expected/horology.out

@@ -1,13 +1,18 @@
 --
 -- HOROLOGY
 --
-SET DateStyle = 'Postgres, MDY';
-SHOW TimeZone;  -- Many of these tests depend on the prevailing setting
+SHOW TimeZone;  -- Many of these tests depend on the prevailing settings
  TimeZone 
 ----------
  PST8PDT
 (1 row)
 
+SHOW DateStyle;
+   DateStyle   
+---------------
+ Postgres, MDY
+(1 row)
+
 --
 -- Test various input formats
 --

src/test/regress/expected/jsonb_jsonpath.out

@@ -2636,15 +2636,6 @@ select jsonb_path_query('[2, true]', '$.string()');
  "true"
 (2 rows)
 
-select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()');
-ERROR:  cannot convert value from timestamptz to timestamp without time zone usage
-HINT:  Use *_tz() function for time zone support.
-select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
-    jsonb_path_query_tz     
-----------------------------
- "Tue Aug 15 00:04:56 2023"
-(1 row)
-
 select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string()');
   jsonb_path_query_array  
 --------------------------
@@ -2657,6 +2648,104 @@ select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string().type()');
  ["string", "string", "string"]
 (1 row)
 
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()');
+ERROR:  cannot convert value from timestamptz to timestamp without time zone usage
+HINT:  Use *_tz() function for time zone support.
+select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
+    jsonb_path_query_tz     
+----------------------------
+ "Tue Aug 15 00:04:56 2023"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
+ERROR:  cannot convert value from timestamp to timestamptz without time zone usage
+HINT:  Use *_tz() function for time zone support.
+select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()'); -- should work
+      jsonb_path_query_tz       
+--------------------------------
+ "Tue Aug 15 12:34:56 2023 PDT"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
+        jsonb_path_query        
+--------------------------------
+ "Tue Aug 15 00:04:56 2023 PDT"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
+      jsonb_path_query      
+----------------------------
+ "Tue Aug 15 12:34:56 2023"
+(1 row)
+
+select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
+ jsonb_path_query 
+------------------
+ "12:34:56+05:30"
+(1 row)
+
+select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
+ jsonb_path_query_tz 
+---------------------
+ "12:34:56-07"
+(1 row)
+
+select jsonb_path_query('"12:34:56"', '$.time().string()');
+ jsonb_path_query 
+------------------
+ "12:34:56"
+(1 row)
+
+select jsonb_path_query('"2023-08-15"', '$.date().string()');
+ jsonb_path_query 
+------------------
+ "08-15-2023"
+(1 row)
+
+set datestyle = 'ISO';
+select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
+   jsonb_path_query_tz    
+--------------------------
+ "2023-08-15 12:34:56-07"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
+     jsonb_path_query     
+--------------------------
+ "2023-08-15 00:04:56-07"
+(1 row)
+
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
+   jsonb_path_query    
+-----------------------
+ "2023-08-15 12:34:56"
+(1 row)
+
+select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
+ jsonb_path_query 
+------------------
+ "12:34:56+05:30"
+(1 row)
+
+select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
+ jsonb_path_query_tz 
+---------------------
+ "12:34:56-07"
+(1 row)
+
+select jsonb_path_query('"12:34:56"', '$.time().string()');
+ jsonb_path_query 
+------------------
+ "12:34:56"
+(1 row)
+
+select jsonb_path_query('"2023-08-15"', '$.date().string()');
+ jsonb_path_query 
+------------------
+ "2023-08-15"
+(1 row)
+
+reset datestyle;
 -- Test .time()
 select jsonb_path_query('null', '$.time()');
 ERROR:  jsonpath item method .time() can only be applied to a string

src/test/regress/sql/horology.sql

@@ -1,9 +1,9 @@
 --
 -- HOROLOGY
 --
-SET DateStyle = 'Postgres, MDY';
 
-SHOW TimeZone;  -- Many of these tests depend on the prevailing setting
+SHOW TimeZone;  -- Many of these tests depend on the prevailing settings
+SHOW DateStyle;
 
 --
 -- Test various input formats

src/test/regress/sql/jsonb_jsonpath.sql

@@ -598,10 +598,28 @@ select jsonb_path_query('1234', '$.string()');
 select jsonb_path_query('true', '$.string()');
 select jsonb_path_query('1234', '$.string().type()');
 select jsonb_path_query('[2, true]', '$.string()');
-select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()');
-select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
 select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string()');
 select jsonb_path_query_array('[1.23, "yes", false]', '$[*].string().type()');
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()');
+select jsonb_path_query_tz('"2023-08-15 12:34:56 +5:30"', '$.timestamp().string()'); -- should work
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
+select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()'); -- should work
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
+select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
+select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
+select jsonb_path_query('"12:34:56"', '$.time().string()');
+select jsonb_path_query('"2023-08-15"', '$.date().string()');
+
+set datestyle = 'ISO';
+select jsonb_path_query_tz('"2023-08-15 12:34:56"', '$.timestamp_tz().string()');
+select jsonb_path_query('"2023-08-15 12:34:56 +5:30"', '$.timestamp_tz().string()');
+select jsonb_path_query('"2023-08-15 12:34:56"', '$.timestamp().string()');
+select jsonb_path_query('"12:34:56 +5:30"', '$.time_tz().string()');
+select jsonb_path_query_tz('"12:34:56"', '$.time_tz().string()');
+select jsonb_path_query('"12:34:56"', '$.time().string()');
+select jsonb_path_query('"2023-08-15"', '$.date().string()');
+reset datestyle;
 
 -- Test .time()
 select jsonb_path_query('null', '$.time()');