I have three tables is question. categories, vocabulary & tex. I am trying to figure out how to have multiple joins in my query, i thought you can just add as many joins as you wanted, as long as you reference them properly.
So, the following two work perfectly on there own:
1.
SELECT
categories.ID AS ID,
categories.ParentID AS ID,
vocabulary.value AS Name
FROM categories
INNER JOIN vocabulary
ON categories.sid=vocabulary.sid
WHERE vocabulary.langid=1
2.
SELECT
categories.ID AS ID,
categories.ParentID AS ID,
tex.value AS Description
FROM categories
INNER JOIN tex
ON categories.tid=tex.tid
WHERE tex.langid=1
However, if i try to combine them as follows, it does not work.
categories.ID AS ID,
categories.ParentID AS ID,
vocabulary.value AS Name
tex.value AS Description
FROM categories
INNER JOIN tex
ON categories.tid=tex.tid
WHERE tex.langid=1
INNER JOIN vocabulary
ON categories.sid=vocabulary.sid
WHERE vocabulary.langid=1
Any ideas?
Thanks in advance
John
In MySQL, when you have columns with the same name, one of them will only be shown. You need to identify them uniquely by supplying ALIAS. And you can either put the condition on the ON clause or WHERE clause which could yield the same result since it uses INNER JOIN.
SELECT categories.ID AS CategoryID,
categories.ParentID AS CategoryParentID,
vocabulary.value AS Name
tex.value AS Description
FROM categories
INNER JOIN tex
ON categories.tid = tex.tid
INNER JOIN vocabulary
ON categories.sid = vocabulary.sid
WHERE vocabulary.langid = 1 AND
tex.langid = 1
Related
I'm making a mySql SELECT:
SELECT name, description, brand, Providers.name, Categories.name, sellingPrice, quantity
FROM Products
INNER JOIN Providers ON Products.idProvider = Providers.id
INNER JOIN Categories ON Products.idCategory = Categories.id
WHERE category = 'tools';
but I become this error:
Error Code: 1052. Column 'name' in field list is ambiguous
even if I specified 'Table.column' (Providers.name, Categories.name).
Some help please ??
Did you try removing the name field in the beginning? Try this code
SELECT description, brand, Providers.name, Categories.name, sellingPrice, quantity
FROM Products
INNER JOIN Providers ON Products.idProvider = Providers.id
INNER JOIN Categories ON Products.idCategory = Categories.id
WHERE category = 'tools';
Similarly provide proper Table.Column mapping in the select.
If you have a name field in Products table, include Products.name in select
Whenever you join tables , you may find same column names in multiple tables. The SQL Engine doesnt know which to pick.So in order to differentiate you need to specify proper mappings. You can also specify simple Alias names instead of full Table names.
Simple rule: Qualify all column names when you write a query. Always.
If you give tables reasonable aliases, this is easy. So your query should look something like this:
SELECT p.name, p.description, p.brand, pr.name, c.name, p.sellingPrice, p.quantity
FROM Products p JOIN
Providers pr
ON p.idProvider = pr.id JOIN
Categories c
ON p.idCategory = c.id
WHERE c.category = 'tools';
I am guessing what tables the columns are coming from, so the qualified names may not be correct (your question doesn't provide this information).
I have an elementary question about SQL query with joining the same table twice. It sounds very simple, but I have some troubles with it. I hope, anyone can help me with this issue :)
I have two little tables: "peoples" (columns: id, name, ...) and "likes" (id, who, whom). People may set the "likes" to each other. The relationship is many to many.
I want get the table with peoples likes: count of received "likes", delivered and count of mutual likes.
All is correctly, when I use only one join. But for two joins (or more) MySQL combine all rows (as expected) and I get wrong values in counts. I don't know, how I must use count/sum/group-by operators in this case:( I would like to do this without subqueries in one query.
I used a query like this:
SELECT *, count(l1.whom), count(l2.whom)
FROM people p
LEFT JOIN likes l1 ON l1.who = p.id
LEFT JOIN likes l2 ON l2.whom = p.id
GROUP BY p.id;
SELECT p.id, name,
count(lwho.who) delivered_likes,
count(lwhom.whom) received_likes,
count(lmut.who) mutual_likes
FROM people AS p
LEFT JOIN likes AS lwho ON p.id = lwho.who
LEFT JOIN likes AS lwhom ON lwhom.id = lwho.id
LEFT JOIN likes AS lmut ON lwhom.who = lmut.whom AND lwhom.whom = lmut.who
GROUP BY p.id;
But it's calculated the counts of likes incorrect.
It's issue just for training and performance is not important, but I guess, that three joins in my last query is too much. Can I do it using 2 joins?
Thanks in advance for help.
I surmise that there is a 1:N relationship between people and likes.
One problem with your second query, as far as I can tell, is that the lwhom correlation of likes is joined to lwho via id=id. Basically lwhom is lwho. I'd recommend changing the ON clause for this correlation from lwhom.id = lwho.id to p.id = lwhom.whom.
The counts will still be affected by the JOINs, however. Supposing that you have an ID column in the likes table, though, you could then have each COUNT tally the distinct Like IDs per person – if not, consider just using COUNT(DISTINCT correlation.*) instead.
Digressions aside, the following should hopefully work:
SELECT p.id, name,
count(distinct lwho.id) delivered_likes,
count(distinct lwhom.id) received_likes,
count(distinct lmut.id) mutual_likes
FROM people AS p
LEFT JOIN likes AS lwho ON p.id = lwho.who
LEFT JOIN likes AS lwhom ON p.id = lwhom.whom
LEFT JOIN likes AS lmut ON lwhom.who = lmut.whom AND lwhom.whom = lmut.who
GROUP BY p.id,p.name;
I have an SQL Fiddle here.
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.
Hi I'm trying to write a query to get information about the author, title, category and medium.
However as the items can be in many mediums and categories, I'm getting the results appearing duplicated in the columns. How can I get the results so I don't see medium as book,book,book and category as Horror,Fantasy,Fiction. I'm assuming I will need some sort of subquery - if so how would I do it?
SELECT book.bookid, book.author, book.title, group_concat(category.categorydesc), group_concat(medium.mediumdesc)
FROM book
Inner JOIN bookscategories ON book.bookid = bookscategories.bookid
Inner JOIN category ON bookscategories.categoryid = category.categoryid
Inner JOIN booksmediums ON book.bookid = booksmediums.bookid
Inner JOIN medium ON booksmediums.mediumid = medium.mediumid
GROUP BY book.bookid
Thanks
Tom
So as stated in comments, solution is to add the DISTINCT keyword in the GROUP_CONCAT() instructions like that:
... book.title, group_concat(DISTINCT category.categorydesc), group_concat(DISTINCT medium.mediumdesc) ...
Here's what I want to accomplish:
Select all rows from table "posts" while also fetching linked entities, such as the author (from table "users") and the names of the categories the post belongs to (from table "categories").
These are my two queries so far:
This one fetches the posts:
SELECT
posts.*
, users.authorName AS author
FROM posts
INNER JOIN users
ON users.id = posts.author
And this one fetches a comma separated list of categories for a specific post:
SELECT
GROUP_CONCAT(categories.category) AS categories
FROM categories
INNER JOIN post_category
ON post_category.categoryID = categories.id
WHERE
post_category.postID = ?
The two queries on their own work fine.
Naturally when the two are combined, I wouldn't need the WHERE clause of the second query.
I tried using the second query as a sub-query within the first one's SELECT clause, but that fetched a comma separated list of ALL categories for ALL posts. I want only the categories for the post I'm currently iterating over.
Any help would be greatly appreciated, and I apologize if any of this is unclear - it's hard enough for me to think about, let alone describe to other people ;)
Something like this:
SELECT posts.*, users.authorName AS author,
GROUP_CONCAT(categories.category) AS categories
FROM posts, users, categories, post_category
WHERE users.id = posts.author
AND post_category.categoryID = categories.id
AND post_category.postID = posts.id
GROUP BY posts.* /* list actual columns here */, author
Or did I miss something?
I think your subquery approach should work fine, but you still need the where clause in your subquery. How else would MySQL know which rows to retrieve? Try:
SELECT posts.*, users.authorName AS author,
(SELECT GROUP_CONCAT(categories.category)
FROM categories
INNER JOIN post_category ON post_category.categoryID = categories.id
WHERE post_category.postID = posts.postID) AS categories
FROM posts
INNER JOIN users ON users.id = posts.author