Postgres 15

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Help with an interesting Postgres question: Why isn't an Index Only Scan used on a partition accessed via the parent table?.
/* 
  utility function to convert from text to various data types
    , such as when you are pulling values out of json 
  The function will cast the value of the first argument 
    to the type of the second argument.
  If the first argument cannot be convert to the target type
    the value of the second argument will be returned as the default.
  If you want to return null as the default, cast the null to the target
    type like `null::integer` or `null::date`
*/
DROP FUNCTION IF EXISTS safe_cast(text, anyelement);
CREATE OR REPLACE FUNCTION safe_cast(text, anyelement)
RETURNS anyelement
LANGUAGE plpgsql as $$
BEGIN
    $0 := $1;
    RETURN $0;
    EXCEPTION WHEN OTHERS THEN
        RETURN $2;
END;
$$;

DROP FUNCTION



CREATE FUNCTION


select
	  safe_cast('true', false::boolean) = true
	, safe_cast('false'::text, false::boolean) = false
	, safe_cast('yes'::text, false::boolean) = true
	, safe_cast('no'::text, false::boolean) = false
	, safe_cast('on'::text, false::boolean) = true
	, safe_cast('off'::text, false::boolean) = false
	, safe_cast('1'::text, false::boolean) = true
	, safe_cast('0'::text, false::boolean) = false
	, safe_cast(1::text, false::boolean) = true
	, safe_cast(0::text, false::boolean) = false
	, safe_cast('foo'::text, false::boolean) = false
	, safe_cast('3'::text, false::boolean) = false
	, safe_cast(3::text, false::boolean) = false
	, safe_cast('', false::boolean) = false
	, safe_cast(null::text, false::boolean) is null
	;


?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?


t
t
t
t
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t
t
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t
t
t



SELECT 1


select
	  safe_cast('123', null::numeric) = 123::numeric
	, safe_cast('123.45', null::numeric) = 123.45::numeric
	, safe_cast('0', null::numeric) = 0::numeric
	, safe_cast('-1', null::numeric) = -1::numeric
	, safe_cast('-1.2', null::numeric) = -1.2::numeric
	, safe_cast('123x', null::numeric) is null
	, safe_cast('', null::numeric) is null
	, safe_cast('foobar', null::numeric) is null
	, safe_cast('123', null::numeric) > 1
    , safe_cast('123', 0::integer) = 123::integer
	, safe_cast('', 0::integer) = 0::integer
	, safe_cast('foo', 0::integer) = 0::integer
	;


?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?


t
t
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t



SELECT 1


select
	  safe_cast('2024-01-02', null::date) = '2024-01-02'::date
	, safe_cast('01-02-2024', null::date) = '2024-01-02'::date
	, safe_cast('2024-01-023', null::date) = '2024-01-23'::date --possibly surprising
	, safe_cast('2024-01-', null::date) is null
	, safe_cast('2024-01-123', null::date) is null
	, safe_cast('2024', null::date) is null
	, safe_cast('foobar', null::date) is null
    , safe_cast('2024-01-02', null::timestamptz) = '2024-01-02 00:00:00'::timestamptz
	;


?column?
?column?
?column?
?column?
?column?
?column?
?column?
?column?


t
f
t
t
t
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t
t



SELECT 1