Fix for DATENAME() gives incorrect value with TZOFFSET part (babelfish-for-postgresql#3846)

Currently, DATENAME function returns a numeric value for TZOFFSET
datepart, which does not match SQL Server's text output.

Root cause: The function definition of sys.datename explicitly calls the
DATEPART function for most argument values, including TZOFFSET, thereby
returning a numerical offset value instead of the required text format
(+/-HH:MM).

Fix: Modified the sys function's SQL definition to extract and return
the timezone offset substring from the input - similar to how the
offset_string is determined in DATETRUNC/DATEBUCKET - if the argument
matches tzoffset. Furthermore, translated the function from SQL language
to plpgsql in order to enable raising an exception for unsupported input
datetime datatypes such as date, time, datetime and smalldatetime.

Task: BABEL-5846
Signed-off-by: Manisha Deshpande <mmdeshp@amazon.com>
(cherry picked from commit debf90b)

Author: manisha-deshpande

contrib/babelfishpg_tsql/sql/sys_functions.sql

@@ -2056,36 +2056,59 @@ LANGUAGE C IMMUTABLE PARALLEL SAFE;
 
 CREATE OR REPLACE FUNCTION sys.datename(IN dp PG_CATALOG.TEXT, IN arg anyelement) RETURNS TEXT AS 
 $BODY$
-SELECT
-    CASE
-    WHEN dp = 'month'::text THEN
-        to_char(arg::sys.DATETIME, 'TMMonth')
+DECLARE
+    date_arg_datatype regtype;
+    result TEXT;
+    datetimeoffset_value sys.datetimeoffset;
+BEGIN
+    date_arg_datatype := pg_typeof(arg);
+
+    IF dp = 'month'::text THEN
+        result := to_char(arg::sys.DATETIME, 'TMMonth');
     -- '1969-12-28' is a Sunday
-    WHEN dp = 'dow'::text THEN
-        to_char(arg::sys.DATETIME, 'TMDay')
+    ELSIF dp = 'dow'::text THEN
+        result := to_char(arg::sys.DATETIME, 'TMDay');
+    ELSIF dp = 'tzoffset'::text THEN
+        IF date_arg_datatype IN ('sys.datetimeoffset'::regtype, 'sys.datetime2'::regtype) THEN
+            -- Explicitly cast to datetimeoffset to validate
+            -- This will throw an error if the timezone offset is invalid
+            datetimeoffset_value := sys.babelfish_conv_string_to_datetimeoffset('DATETIMEOFFSET', arg::TEXT);
+            result := PG_CATALOG.RIGHT(datetimeoffset_value::PG_CATALOG.TEXT, 6);
+        ELSE
+            RAISE EXCEPTION 'The datepart tzoffset is not supported by date function datename for data type %.', date_arg_datatype;
+        END IF;
     ELSE
-        sys.datepart(dp, arg)::TEXT
-    END 
+        result := sys.datepart(dp, arg)::TEXT;
+    END IF;
+    RETURN result;
+END;
 $BODY$
-STRICT
-LANGUAGE sql IMMUTABLE;
+LANGUAGE plpgsql IMMUTABLE;
 
--- Duplicate functions with arg TEXT since ANYELEMENT cannot handle type unknown.
+-- Duplicate function with arg TEXT since ANYELEMENT cannot handle type unknown.
 CREATE OR REPLACE FUNCTION sys.datename(IN dp PG_CATALOG.TEXT, IN arg TEXT) RETURNS TEXT AS
 $BODY$
-SELECT
-    CASE
-    WHEN dp = 'month'::text THEN
-        to_char(arg::date, 'TMMonth')
+DECLARE
+    result TEXT;
+    datetimeoffset_value sys.datetimeoffset;
+BEGIN
+    IF dp = 'month'::text THEN
+        result := to_char(arg::date, 'TMMonth');
     -- '1969-12-28' is a Sunday
-    WHEN dp = 'dow'::text THEN
-        to_char(arg::date, 'TMDay')
+    ELSIF dp = 'dow'::text THEN
+        result := to_char(arg::date, 'TMDay');
+    ELSIF dp = 'tzoffset'::text THEN
+        -- Explicitly cast to datetimeoffset to validate
+        -- This will throw an error if the timezone offset is invalid
+        datetimeoffset_value := sys.babelfish_conv_string_to_datetimeoffset('DATETIMEOFFSET', arg);
+        result := PG_CATALOG.RIGHT(datetimeoffset_value::PG_CATALOG.TEXT, 6);
     ELSE
-        sys.datepart(dp, arg)::TEXT
-    END
+        result := sys.datepart(dp, arg)::TEXT;
+    END IF;
+    RETURN result;
+END;
 $BODY$
-STRICT
-LANGUAGE sql IMMUTABLE;
+LANGUAGE plpgsql IMMUTABLE;
 
 -- These come from the built-in pg_catalog.count in pg_aggregate.dat
 CREATE AGGREGATE sys.count(*)

contrib/babelfishpg_tsql/sql/upgrades/babelfishpg_tsql--4.6.0--4.7.0.sql

@@ -977,6 +977,62 @@ END; $BODY$
 LANGUAGE plpgsql
 STABLE;
 
+CREATE OR REPLACE FUNCTION sys.datename(IN dp PG_CATALOG.TEXT, IN arg anyelement) RETURNS TEXT AS 
+$BODY$
+DECLARE
+    date_arg_datatype regtype;
+    result TEXT;
+    datetimeoffset_value sys.datetimeoffset;
+BEGIN
+    date_arg_datatype := pg_typeof(arg);
+
+    IF dp = 'month'::text THEN
+        result := to_char(arg::sys.DATETIME, 'TMMonth');
+    -- '1969-12-28' is a Sunday
+    ELSIF dp = 'dow'::text THEN
+        result := to_char(arg::sys.DATETIME, 'TMDay');
+    ELSIF dp = 'tzoffset'::text THEN
+        IF date_arg_datatype IN ('sys.datetimeoffset'::regtype, 'sys.datetime2'::regtype) THEN
+            -- Explicitly cast to datetimeoffset to validate
+            -- This will throw an error if the timezone offset is invalid
+            datetimeoffset_value := sys.babelfish_conv_string_to_datetimeoffset('DATETIMEOFFSET', arg::TEXT);
+            result := PG_CATALOG.RIGHT(datetimeoffset_value::PG_CATALOG.TEXT, 6);
+        ELSE
+            RAISE EXCEPTION 'The datepart tzoffset is not supported by date function datename for data type %.', date_arg_datatype;
+        END IF;
+    ELSE
+        result := sys.datepart(dp, arg)::TEXT;
+    END IF;
+    RETURN result;
+END;
+$BODY$
+LANGUAGE plpgsql IMMUTABLE;
+
+-- Duplicate function with arg TEXT since ANYELEMENT cannot handle type unknown.
+CREATE OR REPLACE FUNCTION sys.datename(IN dp PG_CATALOG.TEXT, IN arg TEXT) RETURNS TEXT AS
+$BODY$
+DECLARE
+    result TEXT;
+    datetimeoffset_value sys.datetimeoffset;
+BEGIN
+    IF dp = 'month'::text THEN
+        result := to_char(arg::date, 'TMMonth');
+    -- '1969-12-28' is a Sunday
+    ELSIF dp = 'dow'::text THEN
+        result := to_char(arg::date, 'TMDay');
+    ELSIF dp = 'tzoffset'::text THEN
+        -- Explicitly cast to datetimeoffset to validate
+        -- This will throw an error if the timezone offset is invalid
+        datetimeoffset_value := sys.babelfish_conv_string_to_datetimeoffset('DATETIMEOFFSET', arg);
+        result := PG_CATALOG.RIGHT(datetimeoffset_value::PG_CATALOG.TEXT, 6);
+    ELSE
+        result := sys.datepart(dp, arg)::TEXT;
+    END IF;
+    RETURN result;
+END;
+$BODY$
+LANGUAGE plpgsql IMMUTABLE;
+
 -- Drops the temporary procedure used by the upgrade script.
 -- Please have this be one of the last statements executed in this upgrade script.
 DROP PROCEDURE sys.babelfish_drop_deprecated_object(varchar, varchar, varchar);

test/JDBC/expected/Datetime_system_functions.out

@@ -3292,7 +3292,7 @@ SELECT
 GO
 ~~START~~
 varchar
-FAIL: TZOFFSET issue
+PASS: TZOFFSET works correctly
 ~~END~~
 
 

test/JDBC/expected/datename_tzoffset-before-16_10-or-17_6-vu-cleanup.out

@@ -0,0 +1,11 @@
+DROP TABLE datename_tzoffset_test_cases;
+GO
+
+DROP TABLE datename_stability_test;
+GO
+
+DROP VIEW datename_tzoffset_no_offset_tests_view;
+GO
+
+DROP TABLE datename_tzoffset_different_test_scenarios;
+GO