create or replace function logging_msfunc_strict(text,anyelement)
returns text as
$$
select $1 || '+' || quote_nullable($2)
$$
LANGUAGE sql strict IMMUTABLE;
create or replace function logging_minvfunc_strict(text, anyelement)
returns text as
$$
select $1 || '-' || quote_nullable($2)
$$
LANGUAGE sql strict IMMUTABLE;
create aggregate logging_agg_strict(text)
( stype = text, sfunc = logging_sfunc_strict, mstype = text, msfunc = logging_msfunc_strict, minvfunc = logging_minvfunc_strict
);
create aggregate logging_agg_strict_initcond(anyelement)
( stype = text, sfunc = logging_sfunc_strict, mstype = text, msfunc = logging_msfunc_strict, minvfunc = logging_minvfunc_strict, initcond = 'I', minitcond = 'MI'
);
execute following query:
SELECT p::text || ',' || i::text || ':' || COALESCE(v::text, 'NULL') AS _row, logging_agg_strict (v) OVER w AS nstrict, logging_agg_strict_initcond (v) OVER w AS nstrict
FROM ( VALUES (1, 1, NULL), (1, 2, 'a'), (1, 3, 'b'), (1, 4, NULL), (1, 5, NULL), (1, 6, 'c'), (2, 1, NULL), (2, 2, 'x'), (3, 1, 'z')) AS t (p, i, v) WINDOW w AS (PARTITION BY p ORDER BY i ROWS BETWEEN 1 PRECEDING AND CURRENT ROW);
return following result:
_row | nstrict | nstrict
----------+-----------+---------------- 1,1:NULL | [[null]] | MI 1,2:a | a | MI+'a' 1,3:b | a+'b' | MI+'a'+'b' 1,4:NULL | a+'b'-'a' | MI+'a'+'b'-'a' 1,5:NULL | [[null]] | MI 1,6:c | c | MI+'c' 2,1:NULL | [[null]] | MI 2,2:x | x | MI+'x' 3,1:z | z | MI+'z'
(9 rows)For now I don't understand row 1,4:NULL | a+'b'-'a' | MI+'a'+'b'-'a'. I am not sure why the 1st time you encounter NULL then it will call inverse transition function Overall, not sure about the idea of inverse transition function.