Sql 过滤视图时如何利用基础索引？

我有一个非常简单的查询，执行速度惊人地慢，原因是它在执行连接后对视图进行了扫描。我有点惊讶地看到，因为我希望Postgres在加入之前进行过滤，看到一个底层表在要过滤的列上有一个索引

是否有一种方法可以以某种方式对查询重新排序，或者向计划人员提示如何以不同的方式执行查询

请注意，我确实知道如何通过直接访问底层表来解决这个问题，但是视图隐藏了一点复杂性，最好不要进入查询

询问

解释分析

表和视图定义

编辑： 有人发布了一个答案，该答案随后被删除，其中包含了一个重要的信息：即使基础表中的Conference_id列被索引，视图中的ORDER BY操作也无法实现其目的。不幸的是，我们无法通过这种方式摆脱秩序，因为这是独特的工作所必需的

在…上的区别。。。ORDER BY是性能杀手子查询无法分解 表单_idint REFERENCES _表单id FK缺少索引 aNOT EXISTS antijoin或row\ U number可用于避免不同的子查询

---

@在聊天中，一匹没有名字的马给了我迄今为止最快的解决方案，但从未给出答案。作为参考，这里是他的解决方案，使用横向连接来创建视图

CREATE VIEW form AS
    SELECT f.id, 
        f.encounter_id, 
        f.type, 
        fd.archived, 
        f.cid 
    FROM _form f 
    JOIN LATERAL ( 
        SELECT form_id, archived 
        FROM _form_details _fd 
        WHERE _fd.form_id = f.id 
        ORDER BY _fd.id DESC 
        LIMIT 1 
    ) AS fd ON TRUE; 

这比任何其他解决方案快10倍左右。如果创建为form4，则基于与@wildplasser相同的表，其执行方式如下：

select * from form where encounter_id= 23728 and ztype = 'vitals' ;
Time: 181.065 ms
select * from form2 where encounter_id= 23728 and ztype = 'vitals' ;
Time: 12.395 ms
select * from form3 where encounter_id= 23728 and ztype = 'vitals' ;
Time: 122.305 ms
select * from form4 where encounter_id= 23728 and ztype = 'vitals' ;
Time: 1.305 ms

Postgres 9.3中介绍了一些关于横向连接的好指针：

---

8毫秒对我来说并不是很慢——你需要多快？类似的问题，@a_horse_，没有名字，一切都是相对的。这取决于性能，这意味着它与表单的数量成线性比例。这只是一个测试数据集，我用大约300个表单创建了12000个特定的遭遇id。我预计这些数字中会有一个非常大的倍数，在生产过程中，这个查询每秒运行数百次。注意你的纳秒，查一下。@一匹没有名字的马，它在8毫秒时已经太慢了。我们使用的是10.6版。您是否尝试了类型、名称和id的索引？您是否总是查询相同类型的值？然后使用where type='vitals'筛选索引可能会有所帮助。如果您的类型只有几个不同的值，那么为每个类型创建一个过滤索引也会有所帮助。你的工作价值是什么？如果你增加它会有帮助吗？哇，这真是太少了。我明天要查一下。

CREATE TABLE _form (
  id INT NOT NULL,
  encounter_id INT REFERENCES _encounter (id)            NOT NULL,
  type         TEXT                                      NOT NULL,
  CONSTRAINT pk_form PRIMARY KEY (id),
  FOREIGN KEY (cid) REFERENCES _user_in_role (id)
);

CREATE INDEX encounter_id ON _form (encounter_id, type);

CREATE TABLE _form_details (
  id INT NOT NULL,
  form_id   INT REFERENCES _form (id) NOT NULL,
  archived  BOOLEAN                   NOT NULL DEFAULT FALSE,
  CONSTRAINT pk_form_details PRIMARY KEY (id),
  FOREIGN KEY (cid) REFERENCES _user_in_role (id)
);

CREATE VIEW form AS
  SELECT DISTINCT ON (f.id)
    f.id,
    f.encounter_id,
    f.type,
    fd.archived,
    f.cid
  FROM _form f 
       JOIN _form_details fd 
         ON (f.id = fd.form_id)
  ORDER BY f.id, fd.id DESC;

SET search_path=tmp;
/***/
\i tmp.sql

CREATE TABLE tform (
  id INT NOT NULL
  , encounter_id INT NOT NULL -- REFERENCES tencounter (id)
  , ztype         TEXT                                      NOT NULL
  , CONSTRAINT pk_form PRIMARY KEY (id)
  -- FOREIGN KEY (cid) REFERENCES _user_in_role (id)
);

CREATE TABLE tform_details (
  id INT NOT NULL
  , form_id   INT REFERENCES tform (id) NOT NULL
  , archived  BOOLEAN                   NOT NULL DEFAULT FALSE
  , CONSTRAINT pk_form_details PRIMARY KEY (id)
  -- , FOREIGN KEY (cid) REFERENCES _user_in_role (id)
);

-- ALTER TABLE tform ADD FOREIGN KEY(encounter_id) REFERENCES tencounter (id) ;
CREATE INDEX encounter_id ON tform (encounter_id, ztype);

INSERT INTO tform (id, encounter_id, ztype)
SELECT gs, 23720+gs%29, 'ztype_' || gs::text
FROM generate_series(1,10000) gs
        ;

INSERT INTO tform_details (id, form_id, archived)
SELECT 10000*gs+tf.id, tf.id, (random() > 0.3) ::boolean
FROM tform tf
CROSS JOIN generate_series(0,22) gs
        ;


UPDATE tform
SET ztype = 'vitals'
WHERE random() < 0.2;

/***/
DROP INDEX xxxx ;
CREATE UNIQUE INDEX xxxx ON tform_details (form_id, id);

VACUUM ANALYZE tform;
VACUUM ANALYZE tform_details;

\d tform;
\d tform_details;

select COUNT(*) FROM tform;
select COUNT(*) FROM tform_details;

DROP VIEW form ;
CREATE VIEW form AS
  SELECT DISTINCT ON (f.id)
    f.id
    , f.encounter_id
    , f.ztype
    , fd.archived
    -- , f.cid
  FROM tform f
       JOIN tform_details fd ON f.id = fd.form_id
  ORDER BY f.id, fd.id DESC
        ;

DROP VIEW form2 ;
CREATE VIEW form2 AS
  SELECT f.id
    , f.encounter_id
    , f.ztype
    , fd.archived
  FROM tform f
  JOIN tform_details fd
    ON f.id = fd.form_id
  WHERE NOT EXISTS ( SELECT *
        FROM tform_details nx
        WHERE nx.form_id = fd.form_id
        AND nx.id > fd.id
        )
        ;

DROP VIEW form3 ;
CREATE VIEW form3 AS
  SELECT f.id
    , f.encounter_id
    , f.ztype
    , fd.archived
  FROM tform f
  JOIN ( select xx.form_id, xx.archived
        , row_number() OVER (PARTITION BY xx.form_id ORDER BY xx.id DESC) AS rn
         FROM tform_details xx
        ) fd ON f.id = fd.form_id AND fd.rn = 1
        ;

\echo burn-in
EXPLAIN ANALYZE
select * from form where encounter_id= 23728 and ztype = 'vitals' ;

\echo plain
EXPLAIN ANALYZE
select * from form where encounter_id= 23728 and ztype = 'vitals' ;

EXPLAIN ANALYZE
select * from form2 where encounter_id= 23728 and ztype = 'vitals' ;

EXPLAIN ANALYZE
select * from form3 where encounter_id= 23728 and ztype = 'vitals' ;

\echo no_hash
SET enable_hashjoin = False;

EXPLAIN ANALYZE
select * from form where encounter_id= 23728 and ztype = 'vitals' ;

EXPLAIN ANALYZE
select * from form2 where encounter_id= 23728 and ztype = 'vitals' ;

EXPLAIN ANALYZE
select * from form3 where encounter_id= 23728 and ztype = 'vitals' ;

CREATE VIEW form AS
    SELECT f.id, 
        f.encounter_id, 
        f.type, 
        fd.archived, 
        f.cid 
    FROM _form f 
    JOIN LATERAL ( 
        SELECT form_id, archived 
        FROM _form_details _fd 
        WHERE _fd.form_id = f.id 
        ORDER BY _fd.id DESC 
        LIMIT 1 
    ) AS fd ON TRUE; 

select * from form where encounter_id= 23728 and ztype = 'vitals' ;
Time: 181.065 ms
select * from form2 where encounter_id= 23728 and ztype = 'vitals' ;
Time: 12.395 ms
select * from form3 where encounter_id= 23728 and ztype = 'vitals' ;
Time: 122.305 ms
select * from form4 where encounter_id= 23728 and ztype = 'vitals' ;
Time: 1.305 ms