How to join in MYSQL multiple tables with foreign key relationships including...
Hi I have a central table of resources which are linked to categories and activities by foreign key tables. So the tables are: resources (r): -id -name resources_categories (rc): -resource_id (=r.id...
View ArticleDjango query with joins
I need to write a complex query, which retrieves a lot of data from a bunch of tables. Basically I need to find all instances of the models Customer Payment Invoice where relationships intersect in a...
View ArticleFind records combining two joins
I have three tables: User, House and HouseEvent A House has a foreign_key (user_id) to User and an HouseEvent has a foreign_key (house_id) to House You can see the schema here:...
View Articlewhere clause with includes
I have a User model which has has_many relationship with Identity model. I want to execute includes query with where clause. User.includes(:identities).where("identities.provider = 'facebook') But it...
View ArticleIndex Function using joins
How would I go about creating a function-index to increase the performance of this statement? SELECT COUNT(*) FROM TableName as a, TableName as b WHERE a.first_name = b.first_name AND a.last_name =...
View ArticleMySQL Query with Inner Joins Returning Empty Set
This has really been bugging me for a while. I’m trying to write an SQL query to return all courses (names), their instructors (names),and their prerequisite course (if they exist). But my query just...
View ArticleMysql Delete Statement using joins
I have two tables and would like to delete the first row in the students table but using a join statement. I have tried using delete from student where student.stu_id = (select student_class.stu_id...
View ArticleHow can I run a query that is essentially only two left joins [duplicate]
This question already has an answer here: Full Outer Join in MySQL 6 answers I have two tables and I would like to run a query that does something like this, where both columns can be null: SELECT...
View ArticleSelect by ids using huge “where in” array
I’m working of some kind of items-list class. I’m trying to find a more useful and leightweight way to achieve my goal. So. Current logic and goal. The goal is to select appropriate objects from...
View ArticleBest practice for 1:many joins in Codeigniter fat model, skinny controller?
Say I need to display a list of users and each user which can have many user_roles. The list needs to display: id, username, roles in text eg. 1 | john | member, moderator, admin I have three tables,...
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