有很多关于索引使用的帖子，我试图理解，但我希望有人可以帮助解决我的具体问题。我有一张桌子：
CREATE TABLE f4111
(
costcenter_ilmcu character varying(12), -- Business Unit
documenttype_ildct character varying(2), -- Document Type
ordertype_ildcto character varying(2), -- Order Type
documentorderinvoicee_ildoco numeric, -- Document (Order No Invoice etc.)
datetransactionjulian_iltrdj date, -- Date - Order/Transaction
uniquekeyidinternal_ilukid numeric NOT NULL, -- Unique Key ID (Internal)
CONSTRAINT f4111_pk PRIMARY KEY (uniquekeyidinternal_ilukid)
);
此表有数亿条记录，因此实际内容按年度分区分开：
create table f4111_2011 (
constraint f4111_2011_ck1 check
(datetransactionjulian_iltrdj between '2011-01-01' and '2011-12-31')
) inherits (f4111);
每年都有其中一个，可以追溯到很久。每个分区都有以下索引：
CREATE INDEX f4111_2011_idx5 ON f4111_2011 (documenttype_ildct, ordertype_ildcto);
CREATE INDEX f4111_2011_idx6 ON f4111_2011 (documentorderinvoicee_ildoco);
我的目标是为此表中的15,000个左右工单完成最短交易日期：
create table open_work_orders (
wo numeric not null
)
这有效：
insert into earliest_transaction_dates
SELECT
v.documentorderinvoicee_ildoco, min (v.datetransactionjulian_iltrdj)
FROM
f4111 v
join work_orders w on
v.documentorderinvoicee_ildoco = w.wo
WHERE
v.documenttype_ildct = 'IM' and
v.costcenter_ilmcu = '1AM' and
v.ordertype_ildcto = 'WO' and
v.datetransactionjulian_iltrdj >= '2011-01-01' -- to invoke check constraint
group by
v.documentorderinvoicee_ildoco;
但要产生15,000个预期结果需要9分钟。它似乎没有使用索引f4111_2011_idx6。
这违背了我所珍视的一切，但当我这样做时：
for work_order in select work_order_id from work_orders
loop
insert into earliest_transaction_dates
SELECT
work_order, min (v.datetransactionjulian_iltrdj)
FROM
f4111 v
WHERE
v.documenttype_ildct = 'IM' and
v.costcenter_ilmcu = '1AM' and
v.ordertype_ildcto = 'WO' and
v.documentorderinvoicee_ildoco = work_order and
v.datetransactionjulian_iltrdj >= '2011-01-01';
end loop;
确实使用索引并在2:14结束。
我意识到我在这里缺少一些基本的东西，但有没有办法让查询的9分钟版本使用documentorderinvoicee_ildoco上的索引？
我在9.5.0（太棒了，顺便说一句），我的所有统计数据都是最新的。
---编辑---
根据请求，我添加了以下附加信息。
为了展示手头的问题，我列出的查询是缩写的。每个表实际上都有相当多的字段和更多的索引。我只列出了足以证明问题的字段/索引。
解释计划：
GroupAggregate (cost=2071976.16..2101248.07 rows=21992 width=13)
Group Key: v.documentorderinvoicee_ildoco
-> Merge Join (cost=2071976.16..2096083.48 rows=988933 width=13)
Merge Cond: (((w.wo)::numeric) = v.documentorderinvoicee_ildoco)
-> Sort (cost=1584.03..1622.58 rows=15422 width=4)
Sort Key: ((w.wo)::numeric)
-> Seq Scan on open_work_order_1am w (cost=0.00..511.22 rows=15422 width=4)
-> Materialize (cost=2070392.13..2077443.30 rows=1410233 width=13)
-> Sort (cost=2070392.13..2073917.71 rows=1410233 width=13)
Sort Key: v.documentorderinvoicee_ildoco
-> Append (cost=0.00..1902253.44 rows=1410233 width=13)
-> Seq Scan on f4111_view v (cost=0.00..0.00 rows=1 width=40)
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((documenttype_ildct)::text = 'IM'::text) AND ((costcenter_ilmcu)::text = '1AM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
-> Index Scan using f4111_9999_idx5 on f4111_9999 v_1 (cost=0.14..8.16 rows=1 width=40)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Index Scan using f4111_2017_idx5 on f4111_2017 v_2 (cost=0.14..8.16 rows=1 width=40)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Heap Scan on f4111_2016 v_3 (cost=511.81..13612.41 rows=9453 width=12)
Recheck Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Index Scan on f4111_2016_idx5 (cost=0.00..509.44 rows=20502 width=0)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
-> Bitmap Heap Scan on f4111_2015 v_4 (cost=13279.30..378625.74 rows=277646 width=13)
Recheck Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Index Scan on f4111_2015_idx5 (cost=0.00..13209.89 rows=576546 width=0)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
-> Bitmap Heap Scan on f4111_2014 v_5 (cost=14262.66..400904.20 rows=286705 width=13)
Recheck Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Index Scan on f4111_2014_idx5 (cost=0.00..14190.98 rows=619055 width=0)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
-> Bitmap Heap Scan on f4111_2013 v_6 (cost=13026.39..430799.00 rows=233531 width=13)
Recheck Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Index Scan on f4111_2013_idx5 (cost=0.00..12968.00 rows=567557 width=0)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
-> Bitmap Heap Scan on f4111_2012 v_7 (cost=12008.94..348884.89 rows=256980 width=13)
Recheck Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Index Scan on f4111_2012_idx5 (cost=0.00..11944.69 rows=520026 width=0)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
-> Bitmap Heap Scan on f4111_2011 v_8 (cost=15274.23..329410.87 rows=345915 width=13)
Recheck Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))
Filter: ((datetransactionjulian_iltrdj >= '2011-01-01 00:00:00'::timestamp without time zone) AND ((costcenter_ilmcu)::text = '1AM'::text))
-> Bitmap Index Scan on f4111_2011_idx5 (cost=0.00..15187.75 rows=660732 width=0)
Index Cond: (((documenttype_ildct)::text = 'IM'::text) AND ((ordertype_ildcto)::text = 'WO'::text))