I have a tag name and I need to fetch the tag id from the tags table then lookup all the ids that match the tag id in a taxonomy table and then fetch all the items that match the id in the taxonomy table. Can I do it all in 1 query or will I need a subquery? Here is an example of the database structure
tags database
tid, tag
tags taxonomy database
id, wid, tid
items databse
wid, *
I have the tag from the tags database I need to fetch the tid from the tags database then return all the wid's from the taxonomy database where the tid equals what we just fetched and then return * from the items database. I can get this done running 2 separate queries but I'm looking to do it in just 1.
Thanks
You can just JOIN the tables:
select *
from tags tg
left join taxonomy tx
on tg.tid = tx.tid
left join items i
on tx.wid = i.wid
If you are unfamiliar with JOIN syntax here is a good article:
Visual Explanation of JOINs
Try this:
SELECT *
FROM tags t
INNER JOIN taxonomy t2 ON t2.tid = t.tid
INNER JOIN items i ON i.wid = t2.wid
Note that this will return data only for rows that match in all 3 tables.
Related
I have three tables called Notes another table called Tags and third as a Join table called NoteTagsJoin, Join table holds two foreign keys primary Note id and Primary Tag id. I use this query to get all Notes with tagId:
SELECT * FROM notes INNER JOIN note_tag_join ON notes.entryId = note_tag_join.noteId WHERE note_tag_join.tagId =:tagId
And this query to get all Tags:
SELECT * FROM tags INNER JOIN note_tag_join ON tags.tagId = note_tag_join.tagId WHERE note_tag_join.noteId =:noteId
How can I get Note and all its tags using just Note id with one query?
Are you looking for two joins?
SELECT n.*, t.*
FROM notes n INNER JOIN
note_tag_join nt
ON n.entryId = nt.noteId INNER JOIN
tag t
ON t.tagId = nt.tagId
WHERE n..entryId = :noteId
SELECT * FROM table_name
LEFT JOIN table_name2 ON table_name.id = table_name2.id
LEFT JOIN table_name3 ON table_name2.id = table_name3.id
WHERE table_name.id = id;
Change the "id" with the appropriate id's that you're using. It's important that the id's in the JOINs are coherent, else there will be no link between them.
If you want to select fields of the 3 tables, do this:
SELECT (fields that you want to show) FROM tableA
INNER JOIN tableB ON tableA.commonField = tableB.commonField
INNER JOIN tableC ON tableB.commonField = tableC.commonField
I have an SQL setup akin to the following:
ARTICLES
id (PK)
name
TAGS
id (PK)
tag
...and a third table logging associations between the two, since there can be multiple tags to each article:
ARTICLE_TAG_ASSOCS
id (PK)
article_id (FK)
tag_id (FK)
Via this question I managed to construct a query that would find articles that were tagged with at least one of a number of tags, e.g.
SELECT articles.*
FROM articles
JOIN article_tag_assocs ata ON articles.id = ata.article_id
JOIN tags ON tags.id = ata.tag_id
WHERE tags.tag = 'budgie' OR tags.tag = 'parrot';
Question: How can I alter the above to find articles that match ALL tags, i.e. both 'budgie' and 'parrot', not just one?
Clearly modifying the logic to
WHERE tags.tag = 'budgie' && tags.tag = 'parrot';
...is logically flawed, since MySQL is considering each tag in isolation, one at a time, but hopefully you get what I mean.
There are several workable approaches.
One approach is to perform separate JOIN operations for each tag. For example:
SELECT articles.*
FROM articles
JOIN article_tag_assocs ata
ON ata.article_id = articles.id
JOIN tags ta
ON ta.id = ata.tag_id
AND ta.tag = 'budgie'
JOIN article_tag_assocs atb
ON atb.article_id = articles.id
JOIN tags tb
ON tb.id = atb.tag_id
AND tb.tag = 'parrot'
Note that this can return "duplicate" rows if a given articles is associated to the same tag value more than once. (Adding the DISTINCT keyword or a GROUP BY clause are ways to eliminate the duplicates.)
Another approach, if we are guaranteed that a given article has no duplicate tag values, is to use an inline view to get the list of article_id that are associated with both tags, and then JOIN that set to the articles table. For example:
SELECT a.*
FROM ( SELECT ata.article_id
FROM article_tag_assocs ata
JOIN tags t
ON t.id = ata.tag_id
WHERE t.tag IN ('budgie','parrot')
GROUP BY ata.article_id
HAVING COUNT(1) = 2
) s
JOIN articles a
ON a.id = s.article_id
Note that the literal "2" in the HAVING clause matches the number of values in the predicate on the tag column. The inline view (aliased as s) returns a distinct list of article_id, and we can join that to the articles table.
This approach is useful if you wanted to match, for example, at least three out of four tags. We could use lines like this in the inline view query.
WHERE t.tag IN ('fee','fi','fo','fum')
HAVING COUNT(1) >= 3
Then, any article that matched at least three of those four tags would be returned.
These aren't the only ways to return the specified result, there are several other approaches.
As Roland's answer pointed out, you can also do something like this:
FROM articles a
WHERE a.id IN ( <select article id values related to tag 'parrot'> )
AND a.id IN ( <select article id values related to tag 'bungie'> )
You could also use an EXISTS clause with a correlated subquery, though this approach doesn't usually perform as well with large sets, due to the number of executions of the subquery
FROM articles a
WHERE EXISTS ( SELECT 1
FROM article_tag_assocs s1
JOIN tags t1 ON t1.tag = 'bungie'
WHERE s1.article_id = a.id
)
AND EXISTS ( SELECT 1
FROM article_tag_assocs s2
JOIN tags t2 ON t2.tag = 'parrot'
WHERE s2.article_id = a.id
)
NOTE: in this case, it is possible to reuse the same table aliases within each subquery, because it doesn't lead to ambiguity, though I still prefer distinct aliases because the table aliases show up in the EXPLAIN output, and the distinct aliases make it easier to match the rows in the EXPLAIN output to the references in the query.)
What about this?
Will this give bad performance like EXISTS for large data sets?
This query is to check which rows of 'a1' table has some specified tags and not has some other specified tags
SELECT * FROM a1 WHERE a1.id IN
(SELECT taggables.taggable_id FROM taggables WHERE taggables.taggable_type = 'a1' AND taggables.tag_id IN (1))
AND a1.id NOT IN
(SELECT taggables.taggable_id FROM taggables WHERE taggables.taggable_type = 'a1' AND taggables.tag_id IN (2))
ORDER BY a1.file_count DESC LIMIT 0, 5
I'm having trouble returning more than one 'tag' from the 'catalog_tag' table when I perform a search query for a specific tag. If I do a search on 'catalog.catalog_id', I do get all the associated tags via the inner joins. Is there a way to grab the tags when searching for a specific tag?
Tables:
catalog table has: catalog_id|name|post_date
catalog_tag_relationship has: catalog_id|tag_id
catalog_tag has: tag_id|tag_name
SQL:
SELECT catalog_id, name, tag.tag_id, tag.tag_name
FROM catalog
INNER JOIN catalog_tag_relationship tagRel ON (tagRel.catalog_id=catalog.catalog_id)
INNER JOIN catalog_tag tag ON (tagRel.catalog_tag_id=tag.tag_id)
WHERE (tag.tag_name='dinosaurs')
Revised:
SELECT
catalog.catalog_id,
catalog.name,
tag.tag_id,
tag.tag_name
FROM (
SELECT
catalog.catalog_id as search_id
FROM catalog
INNER JOIN catalog_tag_relationship tagRel
ON tagRel.catalog_id=catalog.catalog_id
INNER JOIN catalog_tag tag ON tagRel.catalog_tag_id=tag.tag_id
WHERE tag_name='dinosaurs'
GROUP BY catalog.catalog_id
) AS searchList
INNER JOIN catalog ON catalog.catalog_id = search_id
INNER JOIN catalog_tag_relationship tagRel
ON tagRel.catalog_id=catalog.catalog_id
INNER JOIN catalog_tag tag ON tagRel.catalog_tag_id=tag.tag_id
EDIT: This should return the same results as choosing a single list from the catalog table.
Step 1: Find list of catalog ID's matching search criteria.
Step 2: Fill in all catalog information for catalog ID's found in step 1.
This will return multiple rows per catalog entry, but only 1 row per unique catalog <-> tag mapping. If you want one row per catalog you'd need GROUP_CONCAT() to see all the different tags for that catalog.
i have a search query which will retrieve information from 3 tables i made the query so it retrieve the information from 2 tables and i don't know if i can combine the third one or not
SELECT *
FROM articles
INNER JOIN terms
ON articles.ArticleID = terms.RelatedID AND terms.TermType = 'article'
the third query is
SELECT * FROM categories where CategoryID in (something)
something is a filed in the articles tables which have value like '3,5,8'
i want do this 2 queries into 1 query and i don't know if it can be done by 1 query or not
without looking at your schema (which would be helpful) and some sample data try this query
SELECT *
FROM categories,articles
INNER JOIN terms
ON (articles.ArticleID = terms.RelatedID AND terms.TermType = 'article')
WHERE
FIND_IN_SET(categories.CategoryID,articles.categories)
here is the definition for FIND_IN_SET()
http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_find-in-set
If i understand you correctly. Looks like you have multiple categories for each article with the Category IDs all stored as a concatenated string.
SELECT A.*
FROM articles A
INNER JOIN terms T on A.ArticleID = T.RelatedID AND T.TermType = 'article'
LEFT JOIN categories C on C.CategoryID IN (3,5,8 OR A.CategoryIDs)
GROUP BY C.CategoryName
You want to LEFT JOIN since you may or may not have multiple categories, you can group by Categories to get disticnt category article pairs and CONCAT() to recombine article records as needed.
I'm trying to load rows form a posts table based on whether they have multiple rows in another table. Take the below table structures:
posts
post_id post_title
-------------------
1 My Post
2 Another Post
post_tags
post_tag_id post_tag_name
--------------------------
1 My Tag
2 Another Tag
postTags
postTag_id postTag_tag_id postTag_post_id
------------------------------------------
1 1 1
2 2 1
Unsurprisingly, post and post_tags stores the posts and tags, and postTags joins which posts have which tags.
What I'd normally do to join the tables is this:
SELECT * FROM (`posts`)
JOIN `postTags` ON (`postTag_post_id` = `post_id`)
JOIN `post_tags` ON (`post_tag_id` = `postTag_tag_id`)
Then I'd have information on the tags, and can have additional stuff later in the query to search tag names for search terms etc, and then GROUP once I have posts that match the search terms.
What I'm trying to do is only select from posts where a post has both tag 1 AND tag 2, and I can't work out the SQL for it. I think it needs to be done in the actual JOIN rather than having a WHERE clause for it as when I run the join above I'd obviously get two rows back, so I can't have something like
WHERE post_tag_id = 1 AND post_tag_id = 2
as each row will only have one post_tag_id, and I can't check different values for the same column in one row.
What I've tried to do is something like this:
SELECT * FROM (`posts`)
JOIN `postTags` ON (postTag_tag_id = 1 AND postTag_tag_id = 2)
JOIN `post_tags` ON (`post_tag_id` = `postTag_tag_id`)
but this is returning 0 results when I run it; I've put conditions like this in JOINS before for similar things and I'm sure it's close but can't quite work out what to do if this doesn't work.
Am I at least on the right track? Hopefully I'm not missing something obvious.
Thanks.
You are trying to ask the postTags row to be at the same time one thing and another.
You either need to do two joins to post_tags and postTags so you get both. Or you can say that the post can have whatever tag between those two and the total amount of tags must equal two (assuming a post cannot related to the same tag more than once).
First approach:
SELECT *
FROM `posts` as p
WHERE p.`post_id` IN (SELECT pt.`postTag_post_id`
FROM `postTags` as pt
WHERE pt.`postTag_tag_id` = 1)
AND p.`post_id` IN (SELECT pt.`postTag_post_id`
FROM `postTags` as pt
WHERE pt.`postTag_tag_id` = 2);
Second approach:
SELECT *
FROM posts as p
WHERE p.post_id IN (SELECT pt.postTag_post_id
FROM (SELECT count(0) as c, pt.postTag_post_id
FROM postTags as pt
WHERE pt.postTag_tag_id IN (1, 2)
GROUP BY pt.postTag_post_id
HAVING c = 2) as pt);
I want also to add that if you use IN or EXISTS in the first approach then you won't have multiple lines for the same post row just because you have more than one tag. This way you save one DISTINCT later that would make your query slower.
I've used an IN in the second approach just as a rule of thumb I use: if you don't need to show the data you don't need to do a JOIN in the FROM section.
SELECT p.*, t1.*, t2.* FROM posts p
INNER JOIN postTags pt1 ON pt1.postTag_post_id = p.id AND pt1.postTag_tag_id = 1
INNER JOIN postTags pt2 ON pt2.postTag_post_id = p.id AND pt2.postTag_tag_id = 2
INNER JOIN post_tags t1 ON t1.post_tag_id = pt1.postTag_tag_id
INNER JOIN post_tags t2 ON t2.post_tag_id = pt2.postTag_tag_id
Without actually building a db the same as yours this is hard to verify but it should work.
Let me start by saying that this type of query is much easier and much more performant in a database that supports analytic queries (Oracle, MS SQL Server). So in MySQL you have to do it the old, crappy, aggregate way.
I also want to say that having a table that stores the names of the tags in post_tags and then the mapping of post tags to posts in postTags is confusing. If it were me, I would change the name of the mapping table to post_tags_map or post_tags_to_post_map. So you would have posts with post_id, post_tags with post_tags_id, and post_tags_map with post_tags_map_id. And those id columns would be named the same in every table. Having the same column that is named differently in other tables is also confusing.
Anyways, let's solve your problem.
First you want a result set that is 1 post id per row, and only the posts that have tags 1 & 2.
select postTag_post_id, count(1) cnt from (
select postTag_post_id from postTags where postTag_tag_id in (1, 2)
) group by postTag_post_id;`
That should give you back data like this:
postTag_post_id | cnt
1 | 2
Then you can join that result set back to your posts table.
select * from posts p,
(
select postTag_post_id, count(1) cnt from (
select postTag_post_id from postTags where postTag_tag_id in (1, 2)
) group by postTag_post_id;
) t
where p.post_id = t.postTag_post_id
and t.cnt >= 2;
If you need to do another join to the post_tags table in order to get the postTag_tag_id from the post_tag_name, your inner most query would change like so:
select postTag_post_id
from postTags a,
post_tags b
where a.postTag_tag_id = b.post_tag_id
and b.post_tag_name in ('tag 1', 'tag 2');
That should do the trick.
Assuming you already know tag IDs (1 and 2), you could do something like this:
SELECT post_id, post_title
FROM posts JOIN postTags ON (postTag_post_id = post_id)
WHERE postTag_tag_id IN (1, 2)
GROUP BY post_id, post_title
HAVING COUNT(DISTINCT postTag_tag_id) = 2
NOTE: DISTINCT is not necessary if there is an alternate key on postTags {postTag_tag_id, postTag_post_id}, as it should be.
NOTE: If you don't have tag IDs (and just have tag names), you'll need another JOIN (towards the post_tags table).
BTW, you should seriously consider ditching the surrogate PK in the junction table (postTags.postTag_id) and just having the natural PK {postTag_tag_id, postTag_post_id}. InnoDB tables are clustered, and secondary indexes in clustered tables are fatter and slower than in heap-based tables. Also, some queries can benefit from storing posts tagged by the same tag physically close together (or storing tags of the same post close together, if you reverse the PK).