Help with Query. Finding records that have the same relationships (MySQL)
-
16-10-2019 - |
Pergunta
I have a table of Listings that has a many to many relationship with a Taxons table. The table structure looks like this:
listings
----------------
id (int)
name (varchar)
listings_taxons
----------------
listing_id (int)
taxon_id (int)
taxons
----------------
id (int)
name (varchar)
My goal is to select all rows in the listings
table that has a matching list of taxon ids. Each returned listing record must have a relationship with the two taxons, such that I get the record set containing the intersection of records between the two taxons.
Example: I have a listing called "Muffler" and it has the following taxons: "Ford", "Mustang", "Exhaust". If I query for all listings with "Ford" and "Exhaust" I should get all listings that have "Ford" and "Exhaust" as taxons.
How would I construct this query efficiently?
Solução
SELECT B.name
FROM
(
SELECT BB.listing_id id,COUNT(1) taxon_count
FROM
(
SELECT id taxon_id FROM taxons
WHERE name IN ('Ford','Exhaust')
) AA
INNER JOIN listings_taxons BB
USING (taxon_id)
GROUP BY listing_id HAVING COUNT(1) = 2
) A
INNER JOIN listings B USING (id);
Subquery A will bring back all listing_ids that have Ford, Exhaust, or both. Doing the GROUP BY count within Subquery A gives any listing id that has a COUNT(1) of 2 has both Ford and Exhaust taxon ids becasue BB.listing_id would appears twice thus HAVING COUNT(1) = 2. Then Subquery A has an INNER JOIN with listings.
Make sure you have the following indexes
ALTER TABLE listings_taxons ADD INDEX taxon_listing_ndx (taxon_id,listing_id);
ALTER TABLE taxons ADD INDEX name_id_ndx (name,id);
Here is some sample data
drop database if exists nwwatson;
create database nwwatson;
use nwwatson
create table listings
(id int not null auto_increment,
name varchar(25),
primary key (id),
key (name));
create table taxons like listings;
create table listings_taxons
(
listing_id int,
taxon_id int,
primary key (listing_id,taxon_id),
unique key (taxon_id,listing_id)
);
insert into listings (name) values ('SteeringWheel'),('WindShield'),('Muffler'),('AC');
insert into taxons (name) values ('Ford'),('Escort'),('Buick'),('Exhaust'),('Mustard');
insert into listings_taxons values
(1,1),(1,3),(1,5),(2,1),(2,2),(2,3),(2,5),
(3,1),(3,4),(4,2),(4,3),(4,4),(5,1),(5,5);
SELECT * FROM listings;
SELECT * FROM taxons;
SELECT * FROM listings_taxons;
SELECT B.name
FROM
(
SELECT BB.listing_id id,COUNT(1) taxon_count
FROM
(
SELECT id taxon_id FROM taxons
WHERE name IN ('Ford','Exhaust')
) AA
INNER JOIN listings_taxons BB
USING (taxon_id)
GROUP BY listing_id HAVING COUNT(1) = 2
) A
INNER JOIN listings B USING (id);
Here is it executed
mysql> drop database if exists nwwatson;
Query OK, 3 rows affected (0.09 sec)
mysql> create database nwwatson;
Query OK, 1 row affected (0.00 sec)
mysql> use nwwatson
Database changed
mysql> create table listings
-> (
-> id int not null auto_increment,
-> name varchar(25),
-> primary key (id),
-> key (name)
-> );
Query OK, 0 rows affected (0.08 sec)
mysql> create table taxons like listings;
Query OK, 0 rows affected (0.05 sec)
mysql> create table listings_taxons
-> (
-> listing_id int,
-> taxon_id int,
-> primary key (listing_id,taxon_id),
-> unique key (taxon_id,listing_id)
-> );
Query OK, 0 rows affected (0.08 sec)
mysql> insert into listings (name) values ('SteeringWheel'),('WindShield'),('Muffler'),('AC');
Query OK, 4 rows affected (0.06 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> insert into taxons (name) values ('Ford'),('Escort'),('Buick'),('Exhaust'),('Mustard');
Query OK, 5 rows affected (0.06 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> insert into listings_taxons values
-> (1,1),(1,3),(1,5),(2,1),(2,2),(2,3),(2,5),
-> (3,1),(3,4),(4,2),(4,3),(4,4),(5,1),(5,5);
Query OK, 14 rows affected (0.11 sec)
Records: 14 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM listings;
+----+---------------+
| id | name |
+----+---------------+
| 4 | AC |
| 3 | Muffler |
| 1 | SteeringWheel |
| 2 | WindShield |
+----+---------------+
4 rows in set (0.00 sec)
mysql> SELECT * FROM taxons;
+----+---------+
| id | name |
+----+---------+
| 3 | Buick |
| 2 | Escort |
| 4 | Exhaust |
| 1 | Ford |
| 5 | Mustard |
+----+---------+
5 rows in set (0.00 sec)
mysql> SELECT * FROM listings_taxons;
+------------+----------+
| listing_id | taxon_id |
+------------+----------+
| 1 | 1 |
| 1 | 3 |
| 1 | 5 |
| 2 | 1 |
| 2 | 2 |
| 2 | 3 |
| 2 | 5 |
| 3 | 1 |
| 3 | 4 |
| 4 | 2 |
| 4 | 3 |
| 4 | 4 |
| 5 | 1 |
| 5 | 5 |
+------------+----------+
14 rows in set (0.00 sec)
mysql> SELECT B.name
-> FROM
-> (
-> SELECT BB.listing_id id,COUNT(1) taxon_count
-> FROM
-> (
-> SELECT id taxon_id FROM taxons
-> WHERE name IN ('Ford','Exhaust')
-> ) AA
-> INNER JOIN listings_taxons BB
-> USING (taxon_id)
-> GROUP BY listing_id HAVING COUNT(1) = 2
-> ) A
-> INNER JOIN listings B USING (id);
+---------+
| name |
+---------+
| Muffler |
+---------+
1 row in set (0.00 sec)
mysql>
Give it a Try !!!
Outras dicas
If I understand correctly, you want to perform relational-division. Try this question with lots of different ways to accomplish that: How to filter SQL results in a has-many-through relation.
I would go for the (multiple) JOIN
solution but you can always test with your data and queries:
SELECT
li.*
FROM
listings AS li
JOIN
listings_taxons AS lt1
ON lt1.listing_id = li.id
JOIN
taxons AS t1
ON t1.id = lt1.taxon_id
AND t1.name = 'Ford'
JOIN
listings_taxons AS lt2
ON lt2.listing_id = li.id
JOIN
taxons AS t2
ON t2.id = lt2.taxon_id
AND t2.name = 'Exhaust'
There are many ways to solve this classical case of a relational division.
For a list of taxons (more than just a few), this form is one of the syntactically shortest:
SELECT l.*
FROM (
SELECT lt.listing_id
FROM taxons t
JOIN listings_taxons lt ON lt.taxon_id = t.id
WHERE t.name IN ('Ford', 'Mustang', 'Exhaust')
GROUP BY lt.listing_id
HAVING COUNT(*) = 3
) x
JOIN listings l ON l.id = x.listing_id;
This assumes a UNIQUE
constraint on (listing_id, taxon_id)
in table listings_taxons
.
Compare to other methods under this related question @ypercube already linked to, to find whether it is among the fastest, too.
SELECT listings.*
FROM listings
INNER JOIN listings_taxons ON listings.id = listings_taxons.listing_id
INNER JOIN taxons ON listing_taxons.taxon_id = taxon.id
WHERE taxon.id in
(SELECT taxon_id
FROM taxon
WHERE name LIKE '%whatever%' OR name LIKE '%another%');
Is this what you mean?