Relational model and basic SQL

Transcription

1 Relational model and basic SQL Introduction to Database Design 2011, Lecture 2 Relational model and keys Basic SQL - Creating tables - Inserting rows - Retrieving information - Joins Overview 2

2 Relational databases A logical view of databases, due to E. F. Codd, 1970 Data stored in tables (aka relations) columns (aka attributes) rows (aka tuples) 3 Basic terminology A relation schema is a set of attributes A database schema is a set table names along with corresponding relation schemas A relation instance is a relation schema and a set of tuples 4

3 A candidate key is minimal set of attributes that characterises tuples uniquely A primary key is a chosen candidate key In the instructor table ID is the primary key Keys 5 Composite primary keys Primary keys can consist of more than one attribute Table: classroom building room_number capacity Packard Painter Taylor Watson Watson Primary key consists of building and room_number 6

4 Foreign keys are references to other tables primary keys The instructor table The department table 7 Notation for schemas instructor (ID, name, dept_name, salary) department (dept_name, building, budget) classroom (building, room_number, capacity) 8

5 Schema diagrams 9 SQL

6 Structured Query Language SQL SQL used for many purposes - as a data definition language for defining database schemas - as a data manipulation language for manipulating data - as a query language for retrieving data 11 Data definition in SQL create table instructor! (ID!! varchar(5),! name!!! varchar(20),! dept_name varchar(20),! salary!! numeric(8,2),! primary key (ID),! foreign key (dept_name) references department); create table department! (dept_name varchar(20),! building!! varchar(15),! budget!! numeric(12,2),! primary key (dept_name)); create table classroom! (building!! varchar(15),! room_number!varchar(7),! capacity!! numeric(4,0),! primary key (building, room_number)); 12

7 Foreign keys in MySQL On ITU s MySQL system, the standard engine does not enforce primary keys InnoDB does create table instructor! (ID!!! varchar(5),! name!! varchar(20), dept_name varchar(20),! salary!! numeric(8,2),! primary key (ID),! foreign key (dept_name) references department(dept_name)) ENGINE = InnoDB; create table department! (dept_name varchar(20),! building! varchar(15),! budget!! numeric(12,2),! primary key (dept_name)) ENGINE = InnoDB; Note also, here name of key attribute is specified 13 SQL types SQL type Describes Example int Integers 12 numeric(12,2) decimal number 12,34 varchar(40) text Volvo text text, no size limit Volvo date date time time 09:30 datetime date and time :30 14

8 Inserting one row Inserting many rows Data manipulation in SQL insert into department values ('Biology', 'Watson', '90000'); insert into department values ('Biology', 'Watson', '90000'), ('History', 'Painter', '50000'); Inserts may not break uniqueness constraint for primary keys Alternative syntax insert into department (dept_name, building, budget) values ('Biology', 'Watson', '90000'), ('History', 'Painter', '50000'); 15 Deleting all rows Data manipulation in SQL delete from department; Can also be modified to delete only certain rows Deleting rows and schema drop table department; 16

9 Queries: retrieving information Queries in SQL mysql> select * from classroom; building room_number capacity Packard Painter Taylor Watson Watson rows in set (0.00 sec) 18

10 Queries in SQL mysql> select building, room_number from classroom; building room_number Packard 101 Painter 514 Taylor 3128 Watson 101 Watson rows in set (0.01 sec) 19 Queries in SQL mysql> select building from classroom; building Packard Painter Taylor Watson Watson 5 rows in set (0.01 sec) 20

11 Queries in SQL mysql> select * from classroom where building = 'Watson'; building room_number capacity Watson Watson rows in set (0.00 sec) 21 Queries in SQL mysql> select room_number from classroom where building = 'Watson'; room_number rows in set (0.00 sec) 22

12 Projection in the relational model Projecting on name and salary select name, salary from instructor; 23 Selection in the relational model select * from instructor where salary > 90000; 24

13 Combining selection and projection select name, dept_name from instructor where salary > 90000; First select, then project 25 Operations in the relational model Selection and projection take tables and return tables But result may contain duplicates select dept_name from instructor; 26

14 Can repair this by using keyword distinct Distinct mysql> select dept_name from instructor; dept_name Biology Comp. Sci. Comp. Sci. Comp. Sci. Elec. Eng. Finance Finance History History Music Physics Physics rows in set (0.00 sec) mysql> select distinct dept_name from instructor; dept_name Biology Comp. Sci. Elec. Eng. Finance History Music Physics rows in set (0.00 sec) 27 Selecting on combinations of features mysql> select name from instructor -> where salary > > and dept_name = "Physics"; name Einstein 1 row in set (0.00 sec) mysql> select name from instructor -> where salary > > or dept_name = "Physics"; name Einstein Gold Brandt 3 rows in set (0.00 sec) 28

15 Joins Queries on multiple relations Recall mysql> select * from instructor; ID name dept_name salary Srinivasan Comp. Sci Wu Finance Mozart Music Einstein Physics El Said History Gold Physics Katz Comp. Sci Califieri History Singh Finance Crick Biology Brandt Comp. Sci Kim Elec. Eng rows in set (0.00 sec) mysql> select * from department; dept_name building budget Biology Watson Comp. Sci. Taylor Elec. Eng. Taylor Finance Painter History Painter Music Packard Physics Watson rows in set (0.00 sec) 30

16 Queries on multiple relations mysql> select * from instructor, department; ID name dept_name salary dept_name building budget Srinivasan Comp. Sci Biology Watson Srinivasan Comp. Sci Comp. Sci. Taylor Srinivasan Comp. Sci Elec. Eng. Taylor Srinivasan Comp. Sci Finance Painter Srinivasan Comp. Sci History Painter Srinivasan Comp. Sci Music Packard Srinivasan Comp. Sci Physics Watson Wu Finance Biology Watson Wu Finance Comp. Sci. Taylor Wu Finance Elec. Eng. Taylor Wu Finance Finance Painter Wu Finance History Painter Wu Finance Music Packard Wu Finance Physics Watson Mozart Music Biology Watson Mozart Music Comp. Sci. Taylor Mozart Music Elec. Eng. Taylor Mozart Music Finance Painter Mozart Music History Painter rows in set (0.01 sec) 31 Joining relations mysql> select * from instructor, department -> where instructor.dept_name = department.dept_name; ID name dept_name salary dept_name building budget Srinivasan Comp. Sci Comp. Sci. Taylor Wu Finance Finance Painter Mozart Music Music Packard Einstein Physics Physics Watson El Said History History Painter Gold Physics Physics Watson Katz Comp. Sci Comp. Sci. Taylor Califieri History History Painter Singh Finance Finance Painter Crick Biology Biology Watson Brandt Comp. Sci Comp. Sci. Taylor Kim Elec. Eng Elec. Eng. Taylor rows in set (0.00 sec) 32

17 Natural join mysql> select * from instructor natural join department; dept_name ID name salary building budget Comp. Sci Srinivasan Taylor Finance Wu Painter Music Mozart Packard Physics Einstein Watson History El Said Painter Physics Gold Watson Comp. Sci Katz Taylor History Califieri Painter Finance Singh Painter Biology Crick Watson Comp. Sci Brandt Taylor Elec. Eng Kim Taylor rows in set (0.01 sec) Natural join compares column names Does not depend on foreign keys 33 First compute cartesian product The select only matching tuples Natural joins operationally mysql> select * from instructor natural join department; Finally project to get rid of duplicate attributes 34

18 Selecting on natural joins mysql> select * from instructor natural join department -> where salary > 70000; dept_name ID name salary building budget Biology Crick Watson Comp. Sci Katz Taylor Comp. Sci Brandt Taylor Elec. Eng Kim Taylor Finance Wu Painter Finance Singh Painter Physics Einstein Watson Physics Gold Watson rows in set (0,00 sec) 35 Example Find all students whose advisors make more than $70000 Best advise I can give: - Start by solving an easier problem - Try to gather all the information needed first 36

19 Example mysql> select * from advisor; s_id i_id mysql> select * from student join advisor on student.id = s_id; ID name dept_name tot_cred s_id i_id Shankar Comp. Sci Peltier Physics Levy Physics Zhang Comp. Sci Brown Comp. Sci Chavez Finance Tanaka Biology Aoi Elec. Eng Bourikas Elec. Eng rows in set (0,00 sec) 37 Example mysql> select * from (student join advisor on student.id = s_id) join instructor on i_id = instructor.id; ID name dept_name tot_cred s_id i_id ID name dept_name salary Shankar Comp. Sci Srinivasan Comp. Sci Peltier Physics Einstein Physics Levy Physics Einstein Physics Zhang Comp. Sci Katz Comp. Sci Brown Comp. Sci Katz Comp. Sci Chavez Finance Singh Finance Tanaka Biology Crick Biology Aoi Elec. Eng Kim Elec. Eng Bourikas Elec. Eng Kim Elec. Eng rows in set (0,00 sec) mysql> select student.name -> from (student join advisor on student.id = s_id) join instructor on i_id = instructor.id -> where salary > 70000; name Peltier Levy Zhang Brown Chavez Tanaka Aoi Bourikas 8 rows in set (0,00 sec) 38

20 Example, alternative solution mysql> select * from student, advisor, instructor where student.id = s_id and instructor.id = i_id; ID name dept_name tot_cred s_id i_id ID name dept_name salary Shankar Comp. Sci Srinivasan Comp. Sci Peltier Physics Einstein Physics Levy Physics Einstein Physics Zhang Comp. Sci Katz Comp. Sci Brown Comp. Sci Katz Comp. Sci Chavez Finance Singh Finance Tanaka Biology Crick Biology Aoi Elec. Eng Kim Elec. Eng Bourikas Elec. Eng Kim Elec. Eng rows in set (0,01 sec) mysql> select student.name from student, advisor, instructor -> where student.id = s_id and instructor.id = i_id -> and salary > 70000; name Peltier Levy Zhang Brown Chavez Tanaka Aoi Bourikas 8 rows in set (0,00 sec) 39 Suppose we want to find all information on courses and their prerequisites Renaming mysql> select * from prereq; course_id prereq_id BIO-301 BIO-101 BIO-399 BIO-101 CS-190 CS-101 CS-315 CS-101 CS-319 CS-101 CS-347 CS-101 EE-181 PHY rows in set (0,00 sec) mysql> select * from course; course_id title dept_name credits BIO-101 Intro. to Biology Biology 4 BIO-301 Genetics Biology 4 BIO-399 Computational Biology Biology 3 CS-101 Intro. to Computer Science Comp. Sci. 4 CS-190 Game Design Comp. Sci. 4 CS-315 Robotics Comp. Sci. 3 CS-319 Image Processing Comp. Sci. 3 CS-347 Database System Concepts Comp. Sci. 3 EE-181 Intro. to Digital Systems Elec. Eng. 3 FIN-201 Investment Banking Finance 3 HIS-351 World History History 3 MU-199 Music Video Production Music 3 PHY-101 Physical Principles Physics rows in set (0,00 sec) 40

21 Renaming mysql> select * from course natural join prereq; course_id title dept_name credits prereq_id BIO-301 Genetics Biology 4 BIO-101 BIO-399 Computational Biology Biology 3 BIO-101 CS-190 Game Design Comp. Sci. 4 CS-101 CS-315 Robotics Comp. Sci. 3 CS-101 CS-319 Image Processing Comp. Sci. 3 CS-101 CS-347 Database System Concepts Comp. Sci. 3 CS-101 EE-181 Intro. to Digital Systems Elec. Eng. 3 PHY rows in set (0,00 sec) mysql> mysql> select * from (course natural join prereq) join course on course_id = prereq_id; ERROR 1066 (42000): Not unique table/alias: 'course' mysql> select * from (course natural join prereq) join course as pre on pre.course_id = prereq_id; course_id title dept_name credits prereq_id course_id title dept_name credits BIO-301 Genetics Biology 4 BIO-101 BIO-101 Intro. to Biology Biology 4 BIO-399 Computational Biology Biology 3 BIO-101 BIO-101 Intro. to Biology Biology 4 CS-190 Game Design Comp. Sci. 4 CS-101 CS-101 Intro. to Computer Science Comp. Sci. 4 CS-315 Robotics Comp. Sci. 3 CS-101 CS-101 Intro. to Computer Science Comp. Sci. 4 CS-319 Image Processing Comp. Sci. 3 CS-101 CS-101 Intro. to Computer Science Comp. Sci. 4 CS-347 Database System Concepts Comp. Sci. 3 CS-101 CS-101 Intro. to Computer Science Comp. Sci. 4 EE-181 Intro. to Digital Systems Elec. Eng. 3 PHY-101 PHY-101 Physical Principles Physics rows in set (0,00 sec) 41 Renaming Suppose we want names of departments with budget larger than biology mysql> select * from department; dept_name building budget Biology Watson Comp. Sci. Taylor Elec. Eng. Taylor Finance Painter History Painter Music Packard Physics Watson rows in set (0.00 sec) This doesn t quite work: select dept_name from department, department where budget > budget and dept_name = "Biology"; 42

22 Renaming We need two copies of department, and they need different names mysql> select T.dept_name -> from department as T, department as S -> where T.budget > S.budget -> and S.dept_name = "Biology"; dept_name Comp. Sci. Finance rows in set (0.00 sec) 43 After this week you should Understand concepts of primary and foreign keys Be able to draw schema diagrams Be able to write SQL statements using - create table - insert into - select from... where Explain meaning of simple queries using relational model 44