Many to Many SQL Query for selecting all Images Tagged with certain words
I have 2 Tables in Postgres:
CREATE TABLE "images" (
"id" serial NOT NULL PRIMARY KEY,
"title" varchar(300) NOT NULL,
"relative_url" varchar(500) NOT NULL)
and
CREATE TABLE "tags" (
"id" serial NOT NULL PRIMARY KEY,
"name" varchar(50) N开发者_Go百科OT NULL)
To establish many to many relationship between images and tags I have another table as:
CREATE TABLE "tags_image_relations" (
"id" serial NOT NULL PRIMARY KEY,
"tag_id" integer NOT NULL REFERENCES "tags" ("id") DEFERRABLE INITIALLY DEFERRED,
"image_id" integer NOT NULL REFERENCES "images" ("id") DEFERRABLE INITIALLY DEFERRED)
Now I have to write a query like "select relative_url of all images tagged with 'apple' and 'microsoft' and 'google' "
What can the most optimized query for this?
Here's the working query I wrote:
SELECT i.id, i.relative_url, count(*) as number_of_tags_matched
FROM images i
join tags_image_relations ti on i.id = ti.image_id
join tags t on t.id = ti.tag_id
where t.name in ('google','microsoft','apple')
group by i.id having count(i.id) <= 3
order by count(i.id)
This query will first show the images matching all three tags, then the images matching at least 2 of the 3 tags, finally at least 1 tag.
You'd join images
to tags_image_relations
, then tags_image_relations
to tags
, then filter WHERE
the name
field is IN
a list of tag names desired. It's the simplest, most obvious, and cleanest?
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