Operation in relational algebra or in an RDBMS to partition relations. The inverse of a Cartesian product (CROSS JOIN).

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Get rows that have ALL join criteria

I have three tables growth_spaces, equipment and growth_space_equipment which links the two tables together. I'm trying to write a query to get all growth spaces that have all of the equipment that I ...
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58 views

Select column values linked to exact set of values in another column

Given the below chats_users table in Postgres 9.5, with integer columns chat_id and user_id, I want to find the chat_id associated with an exact set of user_ids, for example: user_id IN (1, 3) => ...
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47 views

Prove or disprove that `T=R÷S` implies `S=R÷T`? [closed]

Prove or disprove: Given that T=R÷S, it is implied that S=R÷T. My attempt: Let us take some R,S tables and we will divide R÷S: step 1: R S ...
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49 views

Finding parent by set of children

Given a many-to-many relationship (product/component), I need to find a product (or all products) that are composed from the given set of components. I can't wrap my head around the SQL query for ...
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1answer
77 views

How to deduplicate SELECT statements in relational division?

I have a query that does a lot of duplicate work: SELECT visitor_id, '1'::text AS filter FROM events WHERE id IN (SELECT event_id FROM params WHERE key = 'utm_campaign' AND value ...
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2answers
44 views

Finding two users with same pair group

I have the following table which details actions of users and the action's parameters: action_id(auto-increment) | user_id | action_name | action_attr1 I want to find which users performed the same ...
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1answer
39 views

Querying on multiple joined rows

I have a table called visits that is structured like so: +----+--------------+-------------+ | id | name | visitor_id | |----+--------------+-------------+ | 1 | event1 | 1 ...
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74 views

Matching a value with every element of a set of values - Postgresql

I'm new in Postgres and I can't achieve what I'm trying to do. I have a list of films in a Films table ID_FILM FILM NAME 1 Terminator 2 Forrest Gump 3 Nueve reinas A ...
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167 views

Find all users who rated all the movies rated by a specific user

So we have the following relational schema: users(user_id, ..) movies(movie_id, ..) ratings(user_id, movie_id, rate) So, we want to find all the users who have rated all the movies which are rated ...
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4answers
145 views

Make IN clause behave like AND clause

I've asked the same question on stackoverlow, but got no answer, so that's why I'm asking it here (I've read that simple sql questions should be asked at SO, but I have no choice). Suppose I have 3 ...
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Active record relation AND filtering [duplicate]

(Edit: since reposted to dba.stackexchange.com and answered there). Suppose I have 3 models: Post, PostCategory and Category. I'm implementing some kind of page with filters where I can filter posts ...
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173 views

What Happens when Cartesian Product is applied to Relations with same attribute name

I understand that the Cartesian product(X) operation on two databases does not need to be UNION compatible.So,if there is a same attribute called name in the two relations R and S where name in R is ...
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Joining and filtering two sets of the same table

I guess this is an easy and stupid question. Consider this MySQL purchase table (where p_id is autoincremented): +---------+-------------+---------------+---------+ | p_id | item_id | user_id ...
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How to find parent rows that have indentical sets of child rows?

Suppose I have structure like this: Recipes Table: RecipeID Name Description RecipeIngredients Table: RecipeID IngredientID Quantity UOM What are some good ways for ...
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896 views

How to represent class table inheritance (current DBMS-specific way please)?

I want to implement class either-or table inheritance (Account, CatAccountDetails, DogAccountDetails) in SQL Server. I found a recommendation for MySQL here (How do I map an IS-A relationship into a ...
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Many-to-one Subselection in single query

I have two tables with a foreign key from T1->T2, in a one-to-many relationship. That is, 1 tuple in table T1 is associated with 0..N tuples in T2. To create a simple example, lets say T1 is Cars, ...
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Help with Query. Finding records that have the same relationships (MySQL)

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 ...