From Clause & Tuples

The from Clause • The from clause lists the relations involved in the query – corresponds to the Cartesian product operation of the relational algebra.

• Find the Cartesian product employee x department select  from employee, department ■   Find the  employee name, deptno and deptname of all employees select name, employee.eno, deptname  from employee, dept  where  employee. eno = dept.eno

Figure 3.3: Tuples inserted into

Figure 3.4:

Tuple Variables

• Tuple variables are defined in the from clause via the use of the as clause. • Find the customer names and their loan numbers for all customers having a loan at some branch.

select customer­name, T.loan­number, S.amount           from borrower as T, loan as S           where T.loan­number = S.loan­number ■    Find the names of all branches that have greater assets than        some branch located in Brooklyn. select distinct T.branch­name     from branch as T, branch as S     where T.assets > S.assets and S.branch­city = ‘Brooklyn’

Set Operations

• Find all customers who have a loan, an account, or both: (select customer­name from depositor) union (select customer­name from borrower) ■    Find all customers who have both a loan and an  (select customer­name from depositor) intersect (select customer­name from borrower) ■   Find all customers who have an account but no loan. (select customer­name from depositor) except (select customer­name from borrower)

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Ordering the Display of List in alphabeticTuples order the names of all customers having a loan in Perryridge branch

select distinct customer-name from borrower, loan where borrower loan-number = loan.loan-number and branch-name = ‘Perryridge’ order by customer-name • We may specify desc for descending order or asc for ascending order, for each attribute; ascending order is the default. – E.g. order by customer-name desc

Example 2 • Sailors (sid,sname, rating,age) • Boats(bid, bname,color) • Reserves(sid,bid ,date) • Refer to attached list for rows