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Midterm Review Lecture 14b 14 Lectures So Far 1. Introduction 2. The Relational Model 3. Disks and Files 4. Relational Algebra 5. File Org, Indexes 6. Relational Calculus 7. SQL 8. Sorting & Joining 9. Optimizing Queries 10.SQL II 11.The ER Model 12.ER -> Relational 13.Functional Dependencies 14.Normalization By Topic • Introduction – what are databases for? (1) • Relational Topics – The Relational Model – basic SQL, Keys, ICs (1) – Relational Algebra (1) – Relational Calculus (1) – SQL (2) – The ER Model (2) – Functional Dependenciesand Normalization (2) • Database Internals – Storing Data: Disks and Files (1) – File Organization and Indexes (1) – External Sorting and Join Algorithms (1) – Query Optimization (1) Introduction – what are databases for? (1) • Definitions of database, DBMS • Useful properties of database systems – A.C.I.D. – Data Modelling – Querying – Levels of Abstraction • Comparing Database Systems to... – WWW – File Systems – Data Processing Programs The Relational Model (1) • • • • • Tables: Rows and Columns Basic SQL Keys ICs Referential Integrity Relational Algebra (1) • • Somewhat Procedural Query Language Basic Ops: – Selection ( s ) (horizontal). • • • • Selects a subset of rows from relation – Projection ( p ) Retains only wanted columns from relation (vertical). – Cross-product ( ) Allows us to combine two relations. – Set-difference ( — ) Tuples in r1, but not in r2. – Union ( ) Tuples in r1 and/or in r2. Other ops: Intersection ( ) Join ( ) – merge 2 tables based on common columns Division ( / ) – used in “for all” queries Relational Calculus (1) • Formal logic as declarative Query Language • {S | SSailors S.rating > 7 R(RReserves R.sid = S.sid R.bid = 103)} • Concentrated on Tuple Relational Calculus • Also talked about Domain Relational Calculus SQL (2) • Data Definition Language (DDL) • Data Manipulation Language (DML) – Range variables in Select clause – Expressions in Select, Where clauses – Set operators between queries: • Union, Intersect, Except/Minus – Set operators in nested queries: • In, Exists, Unique, <op> Any, <op> All – Aggregates: Count, Sum, Avg, Min, Max – Group By – Group By/Having •Other Features Insert Delete Update Null Values – Outer Joins Views Order By Access Control Integrity Constraints The ER Model (2) • A Visual Language for Modelling the Real World • Entities, Relationships, Attributes Functional Dependencies and Normalization (2) • We’ve just talked about this Storing Data: Disks and Files (1) • Laying out fields in records in pages in files • Buffer Management File Organization and Indexes (1) • Heap File vs Sorted File vs B-Tree Index vs Hash Index • What are advantages, disadvantages of each? External Sorting and Join Algorithms (1) • External Sorting – Sort a file of any size using only 3 pages of memory – Understand optimizations with more memory • Join Algorithms – Nested Loops – Indexed Nested Loops – Sort-Merge Join – Hash Join – What are tradeoffs for different algorithms Query Optimization • Query Plans – trees of operations • How to change plan to find more efficient one