问题
I want to retrieve multiple rows using same id's. Therefore having this table "component_property", I would like to have as results 2 records, id's: 8 and 9 according to my SQL query (check below), but of course and retrieving nothing since I'm checking if cp.property_id = 9102
and later and checking if cp.property_id = 8801
which at the same time is impossible.
ID;type_id;name;desc;property_id,value
--------------------------------------
8;3832;"amplifier1";"";8801;"3"
8;3832;"amplifier1";"";9102;"4015"
9;3832;"amplifier2";"";8801;"3"
9;3832;"amplifier2";"";9102;"4016"
This is the query I have at this moment which retrieves nothing.
SELECT c.id, c.type_id, cp.property_id, cp.value
FROM components_component AS c
INNER JOIN components_componentproperty AS cp
ON c.id = cp.component_id
WHERE
(cp.property_id = 9102 AND cp.value IN ('4015', '4016'))
OR
(cp.property_id = 8801 AND cp.value = '3')
AND c.type_id = 3832
component ===> component_property <=== property
component
id serial NOT NULL,
type_id integer NOT NULL,
name character varying(50) NOT NULL,
description character varying(255),
component_property
id serial NOT NULL,
component_id integer NOT NULL,
property_id integer NOT NULL,
value character varying(255),
property
id serial NOT NULL,
code character varying(10),
preferred_name character varying(50),
My expected result would be:
id;name
-------
8;amplifier1
9;amplifier2
回答1:
This is a case of relational division:
SELECT c.id, c.name
FROM components_componentproperty cp1
JOIN components_componentproperty cp2 USING (component_id)
JOIN components_component c ON c.id = cp1.component_id
WHERE cp1.property_id = 9102 AND cp1.value IN ('4015', '4016')
AND cp2.property_id = 8801 AND cp2.value = '3'
AND c.type_id = 3832
GROUP BY c.id;
We have assembled an arsenal of relevant techniques here:
- How to filter SQL results in a has-many-through relation
Check for a large number of properties
You can expand the above query and for a hand full of properties it will be among the fastest possible solutions. For a bigger number it will be more convenient (and also starting to be faster) to go this route:
Example for 5 properties, expand as needed:
SELECT c.id, c.name
FROM (
SELECT id
FROM (
SELECT component_id AS id, property_id -- alias id just to shorten syntax
FROM components_componentproperty
WHERE property_id IN (9102, 8801, 1234, 5678, 9876) -- expand as needed
GROUP BY 1,2
) cp1
GROUP BY 1
HAVING count(*) = 5 -- match IN expression
) cp2
JOIN components_component c USING (id);
The extra step of the inner subquery cp1
is only necessary, because you obviously have multiple entries per (component_id, property_id)
in components_componentproperty
. We could fold cp1
and cp2
into one and check
HAVING count(DISTINCT property_id) = 5
But I expect that to be more expensive, since count(DISTINCT col)
needs one sort operation per row.
For very long lists IN
is a bad choice. Consider:
- Optimizing a Postgres query with a large IN
来源:https://stackoverflow.com/questions/29117449/retrieve-multiple-rows-with-query-using-and-and-or