Today Collection of unrelated stuff Questions? HW –4 -5 & drop lowest –emphasize project Projects Functional Dependencies? –Someone asked why: Keys, Normal forms Relational Algebra/SQL

Projects SQL Server (more on SQL later) –Implement Database (in ms visual studio) ODBC –Control Panel; Establish data source Visual Interdev –Connect to database; make pages; VBScript Microsoft Front Page –c:\programfiles\microsoft front page

How do we get info out of a Database? Customers(CustID,LastName,FirstName) Inventory(TapeID,MovieName) Rentals(CustomerID,TapeID,CkoutDate, Duration)

DBApplications & Theory Need a way to grab data interested in –Query SQL, VHLL-you’ll need it in your projects Relational Algebra- underlying principles –Set of operators to extract info –Doesn’t allow us to form any question we want, but can construct most that we want –Chapter 4.1

SQL Quick example: we’ll see this again Three basic clauses: SELECT, FROM, WHERE SELECT Lastname, MovieName FROM Customers, Rentals WHERE Customers.CustId = Rentals.CustomerID and Rentals.Duration > 30

Quick Look: Relational Algebra Operators: sets as input, new set as output Basic Set Operators –union, intersection, difference, but no complement. (watch comparable sets) Selection Projection Division(not in text) Cartesian Product Joins, combination of cart product/selection Unofficially aggregate functions(not in text)

Set Operations Binary operations –Result is table(set) with same attributes Sets must be compatible! –R1(A1,A2,A3)&R2(B1,B2,B3) –Domain(Ai)=Domain(Bi) Union: all tuples in R1 or R2 Intersection: all tuples in R1 and R2 Difference: all tuples in R1 and not in R2 No complement… what’s the universe?

Selection Grab a subset of the tuples in a relation which satisfy a given condition Unary operation… returns set with same attributes, but ‘selects’ rows Use and, or, not, >, <… to build condition Example

Projection Unary operation, selects columns Returned schema is different, so returned tuples are not subset of original set, like they are in selection Eliminates duplicate tuples Example

Cartesian Product Binary Operation Result is tuples combining any element of R1 with any element of R2, for R1XR2 Schema is union of Schema(R1) & Schema(R2) Example Notice we could do selection on result to get meaningful info!

Join Most often used… Combines two relations, selecting only related tuples Equivalent to a cross product followed by selection Resulting schema has all attributes of the two relations, but one copy of join condition attributes Example