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Midterm Review

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

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Midterm Review

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  1. Midterm Review

  2. Main Topics • ER model • Relational model • Relational Database Design (Theory)

  3. Symbols of ER Diagram

  4. Symbols of ER Diagram (Cont.)

  5. E-R Diagram of a Bank

  6. 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

  7. 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)

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

  9. 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

  10. 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

  11. 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.

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