अलग-अलग निष्पादन समय को फ़िल्टर करते समय एक ही फ़ील्ड का उपयोग क्यों करते हैं? (विभिन्न सूचकांक उपयोग)

समस्या समाधान के रूप में हम इसके अतिरिक्त SELECT . कर सकते हैं PARTITION BY . में उपयोग किए जाने वाले कॉलम के लिए एक उपनाम अभिव्यक्ति। फिर PG अनुकूलन लागू करें और अनुक्रमणिका का उपयोग करें।

प्रश्न का उत्तर यह हो सकता है:यदि समग्र प्रकार का उपयोग किया जाता है . तो PG अनुकूलन लागू नहीं करता है . सूचना के रूप में यह काम करता है:

PARTITION | FILTER | IS USED?
------------------------------
ALIAS     | ORIG   | NO
ALIAS     | ALIAS  | YES
ORIG      | ALIAS  | NO
ORIG      | ORIG   | NO

देखें यह dbfiddle

create table agreement ( ag_id int, name text, cost numeric(10,2) );
create index ag_idx on agreement (ag_id);
insert into agreement (ag_id, name, cost) values ( 1, '333', 22 ),
(1,'333', 33), (1, '333', 7), (2, '555', 18 ), (2, '555', 2), (3, '777', 4);
select * from agreement;

create function initial () 
returns table( agreement_id int, ag agreement ) language sql stable AS $$
select ag_id, t from agreement t;
$$;
select * from initial() t;

explain( analyze, costs, buffers, verbose ) with totals_by_ag as (
  select 
    *,
    sum( (t.ag).cost ) over ( partition by agreement_id ) as total
  from initial() t
)
select * from totals_by_ag t
where (t.ag).ag_id = 1; -- index is NOT USED

explain( analyze, costs, buffers, verbose ) with totals_by_ag as (
  select 
    *,
    sum( (t.ag).cost ) over ( partition by agreement_id ) as total
  from initial() t
)
select * from totals_by_ag t
where agreement_id = 1; -- index is used when alias for column is used

explain( analyze, costs, buffers, verbose ) with totals_by_ag as (
  select 
    *,
    sum( (t.ag).cost ) over ( partition by (t.ag).ag_id ) as total --renamed
  from initial() t
)
select * from totals_by_ag t
where agreement_id = 1; -- index is NOT USED because grouping by original column

explain( analyze, costs, buffers, verbose ) with totals_by_ag as (
  select 
    *,
    sum( (t.ag).cost ) over ( partition by (t.ag).ag_id ) as total --renamed
  from initial() t
)
select * from totals_by_ag t
where (t.ag).ag_id = 1; -- index is NOT USED even if at both cases original column