introduction to data manipulation in sql cis 4301 lecture notes lecture 16 - 21/03/2006

Introduction to Data Manipulation in SQL

CIS 4301

Lecture Notes

Lecture 16 - 21/03/2006

Lecture 16© CIS 4301 - Spring 2006 2

Simple Movie Database Schema

Movie(Title,Year,length,inColor,studioName,producerC#)

StarsIn(MovieTitle,MovieYear,StarName)

MovieStar(Name,address,gender,birthdate)

MovieExec(name,address,Cert#,netWorth)

Studio(Name,address,presC#)


Simple Queries in SQL

SELECTFROMWHEREORDER BY Asks for those tuples of one or more relation that satisfy a condition, order the output (default ascending)

Note, most SQL implementations allow duplicate tuples, i.e., operate on multisets (bags) rather than sets


SQL vs. Rel. Algebra

SELECT A1, A2, ..., An

FROM R1, R2, ..., Rm WHERE conditionis equivalent to relational algebra query:

A1, A2, ..., An (condition (R1 X R2 X ... X Rm)) Returns unnamed relation whose schema is (A1, A2, ..., An)

SQL is case insensitive Case makes a difference inside quotes!


Selection and Projection

Selection: Find all movies produced by Disney in 1990SELECT *FROM MovieWHERE studioName = ‘Disney’ and year = ‘1990’;

Projection: Find all movies produced by Disney in 1990 and return their title and lengthSELECT title, lengthFROM MovieWHERE studioName = ‘Disney’ and year = ‘1990’;


Duplicates

Retained unless use keyword DISTINCT Duplicate removal is an expensive operation

This is a significant difference between SQL and “pure” relational algebra


String Comparison

Use any of the “usual” string comparison operators such as ‘< ’, ‘>’, ‘= ’, …

More useful, pattern matching using “like” Two wildcards: ‘_’ and ‘%’

Find all movies whose title starts with ‘Star’SELECT titleFROM MovieWHERE title LIKE ‘Star%’;

Find all movies with possessive (‘s) in their titleSELECT titleFROM MovieWHERE title LIKE ‘%’’s%’;


Ordering Output

Return tuples in sorted order (by default in ascending order) Use desc if you want descending order

Find all movies produced by Universal in 1973 and return their title and length; sort movies in ascend. order by length then by titleSELECT title, lengthFROM MovieWHERE studioName = ‘Universal’ AND year = ‘1973’

ORDER BY length, title;


Renaming Attributes

Use keyword AS in SELECT clause

SELECT title AS Movie_Title, length AS Movie_Length

FROM MovieWHERE studioName = ‘Disney’ and year = ‘1990’;

SELECT title AS Title, length*0.016667 AS Length, ‘hrs.’ AS inHours

FROM MovieWHERE studioName = ‘Disney’ and year = ‘1990’;


Cartesian Product

Much of the power of rel. query language comes for the ability to combine two or more relations through cartesian product

Form cartesian product by listing each relation in the FROM clause Consider pairs of tuples satisfying conditions in WHERE clause

Find the name of the producer of ‘Star Wars’


Disambiguating Attributes

Method 1: Prefixing the relation name Find stars and movie executives with the same addressSELECT MovieStar.name, MovieExec.nameFROM MovieStar, MovieExecWHERE MovieStar.address = MovieExec.address;

Output:

MovieStar.name MovieExec.name

Jane Fonda Ted Turner



Method 2: Tuple variable Find two stars with the same addressSELECT Star1.name, Star2.nameFROM MovieStar Star1, MovieStar Star2WHERE Star1.address = Star2.address

AND Star1.name< Star2.name; Output:

Star1.name Star2.name

Alec Baldwin Kim Basinger

tuple variable

• Can use tuple variables anytime for convenience and readability!



What would be different if we re-wrote the query as:

SELECT Star1.name, Star2.nameFROM MovieStar Star1, MovieStar Star2WHERE Star1.address = Star2.address

AND Star1.name <> Star2.name; Output:

Star1.name Star2.name

Alec Baldwin Kim Basinger

Kim Basinger Alec Baldwin


Tuple Variables

Tuples variables are always used (implicitly) in SELECT and WHERE clause

If relation appears only once in the FROM clause, we use the relation name as its own tuple variable Relation name R in FROM clause is shorthand for R R


Set Operators Union: union Intersection: intersect Set Difference: minus Eliminate duplicates

Use ALL to retain duplicates: e.g., UNION ALL Find the names and addresses of movie stars who are not also movie execs


Sample Queries Find the address of MGM studios.

Find all stars that appeared either in a movie made in 1988 or a movie with “Dollar” in the title.


Sample Queries

Find the names and addresses of all female movie stars who are also movie executives with a net worth over $10M.


Sample Queries

Which movies are longer than “Star Wars?”


Sample Queries What is the result of the following query if T is empty?

SELECT *FROM MovieWHERE length <= 120 OR length => 120;

introduction to data manipulation in sql cis 4301 lecture notes lecture 16 - 21/03/2006

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