let be a database having the following relational-schemes: R(A,B,D) and S(A,B) with the attributes of same name in the same domain and with the instances r and s respectively. An instance of r An ...

I am really confused about this. I searched a lot of tutorials but i couldnot find a clear answer. A B B D 1 X x 5 2 x y 6 x 4 I want to cross this two tables.A , B, B,d are attributes. A B B...

Does anyone know any good online resources which I can use to practise SQL to relational algebra conversion?

What is the exact difference between relational algebra and relational calculus? At most references, it will be Relational algebra is procedural and calculus is non-procedural. What do these term...

EMPLOYEE(PERSONNAME, STREET, CITY) WORKS(PERSONNAME,COMPANYNAME, SALARY) COMPANY(COMPANYNAME, CITY) MANAGES(PERSONNAME, MANAGERNAME) Find the names of all employees in this database who do not ...

I'm not asking what a relational database is. I'm asking what relational data is. What makes data relational? What are some examples of relational data and of non-relational data that illustr...

What is a Projection, in terms of database theory and NHibernate when using SetProjection()?

What will natural join return in relational algebra if tables don't have attributes with same names? Will it be null or the same as cross join (cross product) (Cartesian product)?

I don't know how to solve the relational algebra questions. Deposit (Branch, Acc-No, Cust-Name, Balance) Loan (Branch, Loan-No, Cust-Name, Balance) Branch (Branch, Assets, Branch-County) Customer...

I'm doing my best to bend my brain around arel and the relational algebra behind it, but how to represent a SELECT DISTINCT is consistently eluding my comprehension. Can anyone explain how to arel:...

It is not clear to me what is the behaviour of a LEFT JOIN if you try to JOIN on a column that may be NULL. E.g. SELECT columns FROM EmployeePayment ep JOIN EmployeePaymentGroup g ON g.group_id...

Here is an example T(A) = RENTED(A,C) / BOATS(C) select distinct R1.A from RENTED R1 where not exists (select * from SAILBOAT S where not exists (select * from RENTED R2 where R1.A = R2....

I am currently working on a homework assignment that requires a selection to occur that pulls out an element containing a specific attribute of maximum value compared to all other records. I've rea...

What is the relational algebra expression of the query below? I couldn't find the expression for "Is Null". SELECT reader.name FROM reader LEFT JOIN book_borrow ON reader.cardid = book_borrow.card...

I am trying to understand how a OUTER UNION works, and why it is only partially compatible. I am aware this operation was created to take union of tuples from two relations if the relation are no...

I have a question regarding relational algebra and how the theta-join, equi-join, and natural-join can be classified in relation to each other. In a comment on stackoverflow.com sqlvogel quotes E....

I'm using LyX to write some Relational Algebra queries. I'm using the \bowtie symbol for the join operation but when I try to put a text in subscript directly under the symbol, I get the following ...

My query includes a having and count or all in. How are these represented in RA/DRC/TRC? Would I have to simplify my SQL query even more? Here is a simplified example: empl(employee (primary key),...

Let's say we have these tables: CREATE TABLE A ( id SERIAL NOT NULL PRIMARY KEY ); CREATE TABLE B ( id SERIAL NOT NULL PRIMARY KEY ); CREATE TABLE Parent ( id SERIAL NOT NULL PRIMARY KEY, aId...

Suppose I have the following relations: Branch (branchNo(PK), street, city, postcode) Staff (staffNo(PK), fName, lName, sex, branchNo(FK)) Not that it matters for this question, but PK = primar...

Suppose I have two tables, which both have user ids. I want to perform an operation that would return all user IDS in table 1 that are not in table 2. I know there has to be some easy way to do thi...

I'm reading CJ Date's SQL and Relational Theory: How to Write Accurate SQL Code, and he makes the case that positional queries are bad — for example, this INSERT: INSERT INTO t VALUES (1, 2,...

Aheo asks if it is ok to have a table with just one column. How about one with no columns, or, given that this seems difficult to do in most modern "relational" DBMSes, a relation with no attribute...

I am studying relational algebra these days and I was wondering... Don't you thing it would be better if a compiler was existed which could compile relational algebra than compiling SQL? In which...

This is a small part of a homework question so I can understand the whole. SQL query to list car prices that occur more than once: select car_price from cars group by car_price having count (car_pr...