Midterm Review

Main Topics ER model Relational model Relational Database Design (Theory)

Symbols of ER Diagram

Symbols of ER Diagram (Cont.)

E-R Diagram of a Bank

Relational Model Relations: schema and instances Attributes: single-valued, domain, keys Set of records: no duplicates, no order Formal query languages: –Relational algebra (RA) –Tuple relational calculus (TRC) Automatic conversion between relational and ER

Relational Algebra Basic operations: –Selection (  ) –Projection (  ) –Cross-product ( x ) –Set difference ( - ) –Union (  ) –Intersection –join Ignore: Aggregate functions, outer, natural and equi-joins (all join conditions will be given)

Tuple Relational Calculus Basic operations: –Tuple Variable –Predicates, for-all, exists, x -> y –Set difference ( - ) –Union (  ) –Intersection

SQL Query Block SELECT select-clause FROM from-clause [WHERE where-clause] [ORDER BY order-by-expression] [GROUP BY group-by-attributes [HAVING condition-for-each-group]] Query blocks may be nested in FROM and WHERE May be connected using UNION, INTERSECT, and EXCEPT Questions will involve 1 level of nesting of subqueries: –Select … From … select … Where … ….AND Select ….. AND …. Select ….. No further Select within these Select statements

SQL Features Duplicates: DISTINCT. Aggregation queries (e.g., max, sum) return a single value, unless there is a group by Group by / Having –Aggregation on an attribute in SELECT returns one value for each group –All non-aggregation attributes in SELECT must appear in GROUP BY If a attribute appears in GROUP BY, it may not necessarily appear in SELECT

Relational Database Design 1NF Functional Dependences –Armstrong’s Axioms –Closure of a set of FD, Closure of an attribute set –Various kinds of keys Decomposition –3NF and BCNF –Lossless Join, FD preserving, etc.