postgresql SQL联接1-许多只查询父行而不查询重复行

g9icjywg  于 2023-08-04  发布在  PostgreSQL
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我有两个表-invoices和invoiceitems。关系是1-多。我的应用程序允许使用查询中的发票项字段查询发票。只退回发票，不退回项目。
例如，我想获取所有包含项目的发票，其名称包含ac，不区分大小写。输出是分页的，因此我执行一个查询以获得满足条件的发票的计数，然后执行另一个查询以获得发票的相应页面。
表格大小为：

  • 发票-65，000条记录
  • 发票项-3，281，518条记录
  • 条款- 5项
  • 代表- 5项目
  • shipVia - 5产品

每张发票最多链接到100个发票项目。
我的问题是我无法为我的查询找出最佳索引：

架构：

CREATE TABLE invoiceitems
(
  id serial NOT NULL,
  invoice_id integer NOT NULL,
  name text NOT NULL,
  ...
  CONSTRAINT invoiceitems_pkey PRIMARY KEY (id),
  CONSTRAINT invoiceitems_invoice_id_fkey FOREIGN KEY (invoice_id)
      REFERENCES invoices (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
);

CREATE INDEX idx_lower_name
  ON invoiceitems
  USING btree
  (lower(name) COLLATE pg_catalog."default" text_pattern_ops);

CREATE TABLE invoices
(
  id serial NOT NULL,
  term_id integer,
  rep_id integer NOT NULL,
  ship_via_id integer,
  ...
  CONSTRAINT invoices_pkey PRIMARY KEY (id),
  CONSTRAINT invoices_rep_id_fkey FOREIGN KEY (rep_id)
      REFERENCES reps (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT invoices_ship_via_id_fkey FOREIGN KEY (ship_via_id)
      REFERENCES shipvia (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT invoices_term_id_fkey FOREIGN KEY (term_id)
      REFERENCES terms (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
);

字符串

计数查询：

SELECT COUNT(DISTINCT(o.id))
FROM invoices o
JOIN invoiceitems items ON items.invoice_id = o.id
LEFT JOIN terms t ON t.id = o.term_id
LEFT JOIN reps r ON r.id = o.rep_id
LEFT JOIN shipVia s ON s.id = o.ship_via_id WHERE LOWER(items.name) LIKE '%ac%';

型

结果：

6518

查询计划

"Aggregate  (cost=107651.35..107651.36 rows=1 width=4)"
"  ->  Hash Join  (cost=3989.50..106010.59 rows=656304 width=4)"
"        Hash Cond: (items.invoice_id = o.id)"
"        ->  Seq Scan on invoiceitems items  (cost=0.00..85089.77 rows=656304 width=4)"
"              Filter: (lower(name) ~~ '%ac%'::text)"
"        ->  Hash  (cost=2859.00..2859.00 rows=65000 width=16)"
"              ->  Seq Scan on invoices o  (cost=0.00..2859.00 rows=65000 width=16)"

型
似乎我在invoiceitems.name字段上的函数索引根本不起作用。我想这是因为我在寻找名字的一部分，这不是名字的严格前缀。我不确定，但似乎我的发票主键索引在这里也不起作用。
我的问题是，我可以优化计数查询和/或我的模式，以提高性能吗？
我必须允许搜索的部分名称，这不是严格的前缀，我也必须支持不区分大小写的搜索。
我返回匹配记录的查询同样糟糕：

SELECT DISTINCT(o.id), t.terms, r.rep, s.ship_via, ...
FROM invoices o
JOIN invoiceitems items ON items.invoice_id = o.id
LEFT JOIN terms t ON t.id = o.term_id
LEFT JOIN reps r ON r.id = o.rep_id
LEFT JOIN shipVia s ON s.id = o.ship_via_id WHERE LOWER(items.name) LIKE '%ac%' LIMIT 100;

型
其计划：

"Limit  (cost=901846.63..901854.13 rows=100 width=627)"
"  ->  Unique  (cost=901846.63..951069.43 rows=656304 width=627)"
"        ->  Sort  (cost=901846.63..903487.39 rows=656304 width=627)"
"              Sort Key: o.id, t.terms, r.rep, s.ship_via, ..."
"              ->  Hash Join  (cost=11509.54..286596.53 rows=656304 width=627)"
"                    Hash Cond: (items.invoice_id = o.id)"
"                    ->  Seq Scan on invoiceitems items  (cost=0.00..85089.77 rows=656304 width=4)"
"                          Filter: (lower(name) ~~ '%ac%'::text)"
"                    ->  Hash  (cost=5491.03..5491.03 rows=65000 width=627)"
"                          ->  Hash Left Join  (cost=113.02..5491.03 rows=65000 width=627)"
"                                Hash Cond: (o.ship_via_id = s.id)"
"                                ->  Hash Left Join  (cost=75.35..4559.61 rows=65000 width=599)"
"                                      Hash Cond: (o.rep_id = r.id)"
"                                      ->  Hash Left Join  (cost=37.67..3628.19 rows=65000 width=571)"
"                                            Hash Cond: (o.term_id = t.id)"
"                                            ->  Seq Scan on invoices o  (cost=0.00..2859.00 rows=65000 width=543)"
"                                            ->  Hash  (cost=22.30..22.30 rows=1230 width=36)"
"                                                  ->  Seq Scan on terms t  (cost=0.00..22.30 rows=1230 width=36)"
"                                      ->  Hash  (cost=22.30..22.30 rows=1230 width=36)"
"                                            ->  Seq Scan on reps r  (cost=0.00..22.30 rows=1230 width=36)"
"                                ->  Hash  (cost=22.30..22.30 rows=1230 width=36)"
"                                      ->  Seq Scan on shipvia s  (cost=0.00..22.30 rows=1230 width=36)"

型
我只限于PostgreSQL。切换到SQL Server不是一个选项。

**EDIT ==

我已经遵循了欧文非常翔实的指示，这是我所拥有的。

索引：

CREATE INDEX invoiceitems_name_gin_trgm_idx ON invoiceitems USING gin (name gin_trgm_ops);

型

带JOIN的count查询，不带额外表：

EXPLAIN ANALYZE SELECT COUNT(DISTINCT(o.id)) 
FROM invoices o 
JOIN invoiceitems items ON items.invoice_id = o.id 
WHERE items.name ILIKE '%ac%';

"Aggregate  (cost=78961.52..78961.53 rows=1 width=4) (actual time=5205.448..5205.450 rows=1 loops=1)"
"  ->  Nested Loop  (cost=0.00..78960.73 rows=316 width=4) (actual time=0.396..5176.761 rows=6518 loops=1)"
"        ->  Seq Scan on invoiceitems items  (cost=0.00..76885.98 rows=316 width=4) (actual time=0.021..4502.043 rows=6518 loops=1)"
"              Filter: (name ~~* '%ac%'::text)"
"              Rows Removed by Filter: 3275000"
"        ->  Index Only Scan using invoices_pkey on invoices o  (cost=0.00..6.56 rows=1 width=4) (actual time=0.012..0.015 rows=1 loops=6518)"
"              Index Cond: (id = items.invoice_id)"
"              Heap Fetches: 6518"
"Total runtime: 5205.509 ms"

型

半连接的count查询：

EXPLAIN ANALYZE SELECT COUNT(1)
FROM   invoices o
WHERE EXISTS (
   SELECT 1
   FROM   invoiceitems i 
   WHERE  i.invoice_id = o.id
   AND    i.name ILIKE '%ac%'
   );

"Aggregate  (cost=76920.43..76920.44 rows=1 width=0) (actual time=5713.597..5713.598 rows=1 loops=1)"
"  ->  Nested Loop  (cost=76886.76..76919.64 rows=316 width=0) (actual time=5583.706..5703.801 rows=6518 loops=1)"
"        ->  HashAggregate  (cost=76886.76..76886.82 rows=5 width=4) (actual time=5583.568..5594.977 rows=6518 loops=1)"
"              ->  Seq Scan on invoiceitems i  (cost=0.00..76885.98 rows=316 width=4) (actual time=0.295..5148.801 rows=6518 loops=1)"
"                    Filter: (name ~~* '%ac%'::text)"
"                    Rows Removed by Filter: 3275000"
"        ->  Index Only Scan using invoices_pkey on invoices o  (cost=0.00..6.56 rows=1 width=4) (actual time=0.006..0.008 rows=1 loops=6518)"
"              Index Cond: (id = i.invoice_id)"
"              Heap Fetches: 6518"
"Total runtime: 5713.804 ms"

型
半连接似乎没有任何效果。为什么？为什么？
（我认为这并不重要，但我删除了lower(invoiceitems.name)上的原始函数索引）。

**EDIT 2=

我想重点介绍fetchrows查询并提供更多的上下文。
首先，用户可以要求根据发票中的任意字段（而不是发票项）对列进行排序。
此外，用户可以提供涉及发票和发票项目字段的过滤器语句的列表。这些过滤器语句捕获通过字符串或数值进行过滤的语义，例如，过滤器可以是“发票项目名称包含‘ac’，发票折扣高于5%”
我很清楚，我不太可能将每个字段都编入索引，我可能只需要索引最常见的字段，如发票项目名称和其他一些字段。
无论如何，以下是我迄今为止对invoices和invoiceitems表的索引：

发票

  • id作为主键
    发票项
  • id作为主键
  • CREATE INDEX invoiceitems_invoice_id_idx ON invoiceitems USING btree (invoice_id);个
  • CREATE INDEX invoiceitems_name_gin_trgm_idx ON invoiceitems USING gin (name COLLATE pg_catalog."default" gin_trgm_ops);个

下面是使用JOIN对发票项进行的获取行查询的分析：

explain analyze
SELECT DISTINCT(o.id), t.terms, r.rep, s.ship_via, ...
FROM invoices o
JOIN invoiceitems items ON items.invoice_id = o.id
LEFT JOIN terms t ON t.id = o.term_id
LEFT JOIN reps r ON r.id = o.rep_id
LEFT JOIN shipVia s ON s.id = o.ship_via_id 
WHERE (items.name ILIKE '%df%' AND items.name IS NOT NULL) LIMIT 100;

"Limit  (cost=79100.70..79106.95 rows=100 width=312) (actual time=4637.195..4637.195 rows=0 loops=1)"
"  ->  Unique  (cost=79100.70..79120.45 rows=316 width=312) (actual time=4637.190..4637.190 rows=0 loops=1)"
"        ->  Sort  (cost=79100.70..79101.49 rows=316 width=312) (actual time=4637.186..4637.186 rows=0 loops=1)"
"              Sort Key: o.id, o.customer, o.business_no, o.bill_to_name, o.bill_to_address1, o.bill_to_address2, o.bill_to_postal_code, o.ship_to_name, o.ship_to_address1, o.ship_to_address2, o.ship_to_postal_code, o.purchase_order_no, t.terms, r.rep, ((o.ship_date)::text), s.ship_via, o.delivery, o.hst_percents, o.sub_total, o.total_before_hst, o.total, o.total_discount, o.hst, o.item_count"
"              Sort Method: quicksort  Memory: 25kB"
"              ->  Hash Left Join  (cost=113.02..79087.58 rows=316 width=312) (actual time=4637.179..4637.179 rows=0 loops=1)"
"                    Hash Cond: (o.ship_via_id = s.id)"
"                    ->  Hash Left Join  (cost=75.35..79043.98 rows=316 width=284) (actual time=4637.123..4637.123 rows=0 loops=1)"
"                          Hash Cond: (o.rep_id = r.id)"
"                          ->  Hash Left Join  (cost=37.67..79001.96 rows=316 width=256) (actual time=4637.119..4637.119 rows=0 loops=1)"
"                                Hash Cond: (o.term_id = t.id)"
"                                ->  Nested Loop  (cost=0.00..78960.73 rows=316 width=228) (actual time=4637.115..4637.115 rows=0 loops=1)"
"                                      ->  Seq Scan on invoiceitems items  (cost=0.00..76885.98 rows=316 width=4) (actual time=4637.108..4637.108 rows=0 loops=1)"
"                                            Filter: ((name IS NOT NULL) AND (name ~~* '%df%'::text))"
"                                            Rows Removed by Filter: 3281518"
"                                      ->  Index Scan using invoices_pkey on invoices o  (cost=0.00..6.56 rows=1 width=228) (never executed)"
"                                            Index Cond: (id = items.invoice_id)"
"                                ->  Hash  (cost=22.30..22.30 rows=1230 width=36) (never executed)"
"                                      ->  Seq Scan on terms t  (cost=0.00..22.30 rows=1230 width=36) (never executed)"
"                          ->  Hash  (cost=22.30..22.30 rows=1230 width=36) (never executed)"
"                                ->  Seq Scan on reps r  (cost=0.00..22.30 rows=1230 width=36) (never executed)"
"                    ->  Hash  (cost=22.30..22.30 rows=1230 width=36) (never executed)"
"                          ->  Seq Scan on shipvia s  (cost=0.00..22.30 rows=1230 width=36) (never executed)"
"Total runtime: 4637.731 ms"

型
下面是使用WHERE EXISTS而不是JOIN对发票项进行的获取行查询的分析：

explain analyze
SELECT o.id, t.terms, r.rep, s.ship_via, ...
FROM invoices o
LEFT JOIN terms t ON t.id = o.term_id
LEFT JOIN reps r ON r.id = o.rep_id
LEFT JOIN shipVia s ON s.id = o.ship_via_id 
WHERE EXISTS (
   SELECT 1
   FROM   invoiceitems i 
   WHERE  i.invoice_id = o.id
   AND    i.name ILIKE '%df%'
   AND    i.name IS NOT NULL
   ) LIMIT 100;

"Limit  (cost=0.19..43302.88 rows=100 width=610) (actual time=5771.852..5771.852 rows=0 loops=1)"
"  ->  Nested Loop Left Join  (cost=0.19..136836.68 rows=316 width=610) (actual time=5771.848..5771.848 rows=0 loops=1)"
"        ->  Nested Loop Left Join  (cost=0.19..135404.33 rows=316 width=582) (actual time=5771.844..5771.844 rows=0 loops=1)"
"              ->  Nested Loop Left Join  (cost=0.19..134052.55 rows=316 width=554) (actual time=5771.841..5771.841 rows=0 loops=1)"
"                    ->  Merge Semi Join  (cost=0.19..132700.78 rows=316 width=526) (actual time=5771.837..5771.837 rows=0 loops=1)"
"                          Merge Cond: (o.id = i.invoice_id)"
"                          ->  Index Scan using invoices_pkey on invoices o  (cost=0.00..3907.27 rows=65000 width=526) (actual time=0.017..0.017 rows=1 loops=1)"
"                          ->  Index Scan using invoiceitems_invoice_id_idx on invoiceitems i  (cost=0.00..129298.19 rows=316 width=4) (actual time=5771.812..5771.812 rows=0 loops=1)"
"                                Filter: ((name IS NOT NULL) AND (name ~~* '%df%'::text))"
"                                Rows Removed by Filter: 3281518"
"                    ->  Index Scan using terms_pkey on terms t  (cost=0.00..4.27 rows=1 width=36) (never executed)"
"                          Index Cond: (id = o.term_id)"
"              ->  Index Scan using reps_pkey on reps r  (cost=0.00..4.27 rows=1 width=36) (never executed)"
"                    Index Cond: (id = o.rep_id)"
"        ->  Index Scan using shipvia_pkey on shipvia s  (cost=0.00..4.27 rows=1 width=36) (never executed)"
"              Index Cond: (id = o.ship_via_id)"
"Total runtime: 5771.948 ms"

型
我没有尝试第三种选择，即按不同的invoice_id对invoiceitems行进行排序，因为这种方法似乎只有在没有给出排序的情况下才可行，而通常情况恰恰相反--存在排序。

postgresql

1条答案

按热度按时间
gzszwxb4

gzszwxb41#

索引

三元索引

使用pg_trgm模块提供的三元组索引，该模块为GIN或GiST索引提供运算符类，以支持所有LIKE和ILIKE模式，而不仅仅是左锚定模式。请参阅：

更多关于如何使用trigram index的信息：

  • PostgreSQL LIKE查询性能变化

示例如下：

CREATE EXTENSION pg_tgrm;  -- only once per db

CREATE INDEX invoiceitems_name_gist_trgm_idx
ON invoiceitems USING gist (name gist_trgm_ops);

字符串
GIN索引可能更快，但也更大。The manual:
根据经验，GIN索引的搜索速度比GiST索引快，但构建或更新速度较慢;因此GIN更适合静态数据，而GiST更适合经常更新的数据。
这一切都取决于确切的要求。

额外的btree索引

当然，在invoiceitems.invoice_id上还需要一个普通的btree索引（默认）：

CREATE INDEX invoiceitems_invoice_id_idx ON invoiceitems (invoice_id);

型

多列索引，仅索引扫描

您可能会从making this index "covering" for an index-only scan中获得一些额外的好处。GIN索引通常对于integer列（如invoice_id）没有意义。但是为了保存额外的堆查找，可能需要将其包含在多列GIN（或GiST）索引中。你得先测试一下。
为此，您需要额外的模块btree_gin（或btree_gist）。GIN示例：

CREATE EXTENSION btree_gin;

CREATE INDEX invoiceitems_name_gin_trgm_idx
ON invoiceitems USING gin (name gin_trgm_ops, invoice_id);

型
这将消除对以上B树索引的需要。但无论如何都要创建它，以加速FK检查，以及用于许多其他目的。

查询

计数

为了一个...
查询以获取发票的数量
......省略只会造成伤害的附加表（如果有的话）：

SELECT COUNT(DISTINCT(item.invoice_id))
FROM   invoiceitems item 
JOIN   invoices o ON item.invoice_id = o.id
LEFT   JOIN terms t ON t.id = o.term_id
LEFT   JOIN reps r ON r.id = o.rep_id
LEFT   JOIN shipVia s ON s.id = o.ship_via_id
WHERE  item.name ILIKE '%ac%';

型
由于外键约束保证了引用完整性，因此您甚至可以在此查询中省略表invoices。你闪亮的新指数应该踢！

返回行

对于退货：
EXISTS在这里仍然很好：

SELECT t.terms, r.rep, s.ship_via, ...
FROM   invoices     o
LEFT   JOIN terms   t ON t.id = o.term_id
LEFT   JOIN reps    r ON r.id = o.rep_id
LEFT   JOIN shipVia s ON s.id = o.ship_via_id
WHERE  EXISTS (
   SELECT FROM invoiceitems i 
   WHERE  i.invoice_id = o.id
   AND    i.name ILIKE '%ac%'
   )
-- ORDER BY ???
LIMIT 100;

型
或者你可以测试这个变量，它作为子选择连接到上面的查询。可能更快：

SELECT t.terms, r.rep, s.ship_via, ...
FROM  (
   SELECT DISTINCT invoice_id
   FROM   invoiceitems
   WHERE  name ILIKE '%ac%'
   ORDER  BY invoice_id           -- order by id = cheapest with above index
   LIMIT  100                     -- LIMIT early!
   ) item
JOIN   invoices     o ON o.id = item.invoice_id
LEFT   JOIN terms   t ON t.id = o.term_id
LEFT   JOIN reps    r ON r.id = o.rep_id
LEFT   JOIN shipVia s ON s.id = o.ship_via_id
-- ORDER BY ???
;

型
本例通过invoice_id获取前100个（因为您没有提供排序顺序）。这一切都取决于细节。。

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