self-join

I need some suggestions from the database design experts here. I have around six foreign keys into a single table (defect) which all point to primary key in user table. It is like: defect (.....,assigned_to,created_by,updated_by,closed_by...) If I want to get information about the defect I can make six joins. Do we have any better way to do it? Another one is I have a states table which can store one of the user-defined set of values. I have defect table and task table and I want both of these tables to share the common state table (New, In Progress etc.). So I created: task (.....,state_id

Can anyone help? I have 1 class, basically it holds Members and within that class is a List. The members i have in a List also... So basically it goes like this, I have 2 members and each member has a number of sessions. I wish to only return each member with 1 Session. I have done a LINQ query, but of course it doesn't work... I think i need to do a self join, any ideas? Basically my error is m doesn't exist in my subquery self join. var sessions = from m in this.members join s in ( from se in m.Sessions group se by se.Name into g select new {Name = g.Key, SessioEndTime = g.Max(a=>a

I am trying to run a query that joins a table against itself and does fuzzy string comparison (using trigram comparisons) to find possible company name matches. My goal is to return records where the trigram similarity of one record's company name (ref_name field) matches another record's company name. Currently, I have my threshold set to 0.9 so it will only bring back matches that are very likely to contain the a similar string. I know that self joins can result in many comparisons by nature, but I want to optimize my query the best I can. I don't need results instantaneously, but currently

There are two tables: table A and table B. They have the same columns and the data is practically identical . They both have auto-incremented IDs, the only difference between the two is that they have different IDs for the same records. Among the columns, there is an IDENTIFIER column which is not unique , i.e. there are (very few) records with the same IDENTIFIER in both tables. Now, in order to find a correspondence between the IDs of table A and the IDs of table B, I have to join these two tables (for all purposes it's a self-join) on the IDENTIFIER column, something like: SELECT A.ID, B.ID

I have a table like Employee ================== name salary ================== a 10000 b 20000 c 5000 d 40000 i want to get all the employee whose salary is greater than A's salary. I don't want to use any nested or sub query. It has been asked in an interview and hint was to use self join. I really can't figure out how to achieve the same. select e1.* from Employee e1, Employee e2 where e2.name = 'a' and e1.salary > e2.salary Using self join select e1.* from Employee e1 join Employee e2 on e2.name = 'a' and e1.salary > e2.salary Chinjoo SELECT emp1.* FROM Employee emp1 JOIN Employee emp2 ON

I have an ActiveRecord called Name which contains names in various Languages . class Name < ActiveRecord::Base belongs_to :language class Language < ActiveRecord::Base has_many :names Finding names in one language is easy enough: Language.find(1).names.find(whatever) But I need to find matching pairs where both language 1 and language 2 have the same name. In SQL, this calls for a simple self-join: SELECT n1.id,n2.id FROM names AS n1, names AS n2 WHERE n1.language_id=1 AND n2.language_id=2 AND n1.normalized=n2.normalized AND n1.id != n2.id; How can I do a query like this with ActiveRecord?

I have a MySQL database with these two tables: Tutor(tutorId, initials, lastName, email, phone, office) Student(studentId, initials, lastName, email, tutorId) What is the query to return the initials and last names of any student who share the same tutor? I tried SELECT intials, lastName FROM Student WHERE tutorId = tutorId but that just returns the names of all students. You'll have to join students against itself: SELECT s1.initials, s1.lastName FROM Student s1, Student s2 WHERE s1.studentId <> s2.studentID /* Every student has the same tutor as himself */ AND s1.tutorId = s2.tutorid If you