Database Systems. Bence Molnár

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1 Database Systems Bence Molnár

2 SQL

3 History Beginning of 70s IBM SEQUEL (Structured English QUery Language) Structured/Standard Query Language In 1986 ANSI, 1987 ISO standard SQL2 ('92), SQL3 ('99),... Development goes on (SQL2011) It's a standard, more or less all DBMS support it Relational Software, Inc. Oracle Corp.

4 Basics Core of SQL is equivalent with relational algebra, however SQL extends it: Summarize operations (e.g. SUM, AVG) Database modification A non-procedural language (declarative), so we need to describe what we want to do, instead of to describe how to do it. Data Description Language (DDL), Data Modification Language (DML), Data Control Language (DCL), Date Query Language (DQL)

5 Relational algebra vs. SQL

6 SQL basics Creating a database: CREATE DATABASE dbname; permissions user Host (access location) character coding (UTF8, LATIN2 [ISO ]) templates (ie. Spatial data storage) Selecting DB: Defined during the connection (only one db) USE dbname; Allowed characters: [_a-z0-9]

7 Reminder Relational database schema Relational schema: Table(ID: Serial, Name: Text, Age: Integer) Relational database schema: Table ID: Serial Name: Text Age:Integer...

8 Creating tables CREATE TABLE students ( neptun VARCHAR(6) [...], name VARCHAR(50), age INTEGER, average DOUBLE PRECISION, PRIMARY KEY (neptun) );

9 Creating tables CREATE TABLE tablename : DEFAULT NULL /NOT NULL UNIQUE (!= PRIMARY KEY!) AUTO INCREMENT/Sequence/AutoNumber

10 Modifying tables ALTER TABLE tablename ADD columnname type; ALTER TABLE tablename DROP columnname; DROP students; TRUNCATE tablename; ALTER TABLE students RENAME TO bme_students; DROP tablename; ALTER TABLE students DROP name; ALTER TABLE tablename RENAME TO new_tablename; ALTER TABLE students ADD place_of_birth VARCHAR(50); TRUNCATE students; If an other table/attribute depends(relates) to the altered information, you have to change those as well!

11 Upload Insert INSERT INTO tablename [(attribute1, attribute2, )] VALUES (value1, value2, ); INSERT INTO students (neptun, name, age, average) VALUES ('ABCDEF', 'Thomas Scott', 23, 4.5); LOAD DATA COPY

12 Data modification Modification UPDATE tablename SET attribute = value WHERE condition; UPDATE students SET average = 4.6 WHERE name = 'Alexander Burrs'; Deletion DELETE FROM tablename WHERE condition; DELETE FROM students 'Alexander Burrs'; WHERE name =

13 Projection in SQL Projection [π, Π]: defined attributes of relation is kept, rest are removed while the new relation is created. SELECT name, age FROM students; neptun SELECT name age * FROM students; neptun name age

14 Simple queries SELECT attribute(s) FROM table(s) WHERE condition(s); SELECT name FROM students WHERE name = 'Alexander Burrs'; Attributes and tables are separated by comas Line ends with semicolon Conditions are joined by logical operators Operators: =, <>, >, <, =>, <=, LIKE, BETWEEN, IN, NOT DISTINCT Aliases (AS) Special characters: *, _, % (MS Access: *,?, #) Escape characters Quotes: ', " Uppercase and lowercase (case sensitive) Reserved keywords

15 Views CREATE TABLE: physically storing the data CREATE VIEW viewtable AS query; CREATE VIEW students_a AS SELECT * FROM students WHERE name LIKE 'A%'; Only definition is stored without data You can query a view as well Editable? (materialized view) DROP VIEW viewtable;

16 Order SELECT * FROM students WHERE name LIKE 'Smith%' ORDER BY place_of_birth ASC/DESC; neptun name date_of_birth neptun name date_of_birth Abádszalók Zalaegerszeg Abádszalók Zalaegerszeg Almásfüzitő Záhony Budapest Záhony

17 Grouping Group records based on equal attributes to manage them together SELECT AVG(grade) FROM students WHERE class = 'Database Systems' GROUP BY age; Condition on a grouped attribute SELECT AVG(grade) FROM students WHERE class = 'Database Systems' GROUP BY age HAVING AVG(grade) >= 3;

18 name year fgrade Kiss Pista Nagy Jenő Kertész Ágnes Bíró Gabriella Szántó Jóska Tóth Barna Sándor Lívia SELECT year, AVG(grade) FROM students GROUP BY year; year grade

19 name year grade Kiss Pista Nagy Jenő Kertész Ágnes Bíró Gabriella Szántó Jóska Tóth Barna Sándor Lívia SELECT year, AVG(grade) FROM students GROUP BY year; year 1990 grade SELECT year, AVG(grade) FROM students WHERE grade>3 GROUP BY year; Filter on original rows year grade

20 name year grade Kiss Pista Nagy Jenő Kertész Ágnes Bíró Gabriella Szántó Jóska Tóth Barna Sándor Lívia SELECT year, AVG(grade) FROM students GROUP BY year; year 1990 grade SELECT year, AVG(grade) FROM students WHERE grade>3 GROUP BY year; Filter on original rows year SELECT year, AVG(grade) FROM students GROUP BY year HAVING AVG(grade)>=4; year grade Filter on agregated rows grade

21 Functions SELECT COUNT(*) FROM students; SELECT AVG(grade) FROM students; SELECT MIN(grade) FROM students; SELECT MAX(grade) FROM students; SELECT SUM(grade)/COUNT(*) FROM students WHERE grade IS NOT NULL; SELECT DISTINCT date_of_birth FROM students;

22 String functions SELECT firstname " " lastname FROM students; SELECT * FROM students WHERE firstname " " lastname = "Tim John"; MySQL (MariaDB): CONCAT() PgSQL: Access: & SELECT * FROM courses WHERE SUBSTRING(code FROM 6 TO 7)="FT";

23 Free-text search field LIKE 'string' SELECT * FROM students WHERE name LIKE 'John%'; Joker characters_ %: any character, any length (0, 1, many) _: any single character

24 Advanced queries SELECT name FROM students WHERE (name LIKE 'Peter%' OR name LIKE 'Alexander%') AND name LIKE '%Great'; SELECT name FROM students WHERE name LIKE 'Kov_cs%'; SELECT class_length*60 AS minutes FROM class; SELECT name FROM students WHERE class = 'Database Systems' AND NOT failed;

25 Intersection / Union General form: (SELECT neptun FROM name LIKE 'Great%') students WHERE (SELECT neptun FROM students place_of_birth = 'Budapest'); WHERE INTERSECT/UNION syntax Number of attributes

26 Subselect moves(title, directorid) year, length, studioname, directors(id, name, address, income) SELECT name FROM directors WHERE ID = (SELECT directorid FROM movies WHERE title = 'Lord of the Rings'); SELECT * FROM movies WHERE directorid IN (SELECT ID FROM directors WHERE name LIKE 'P_ter%');

27 Accessing multiple tables movies(title, directorid) year, length, studioname, directors(id, name, address, income) SELECT address, name FROM directors, movies; (?) SELECT address, name FROM directors, movies WHERE movies.directorid = director.id;

28 Relationships Natural join Based on equal attribute names No other condition Only a single equal attribute is included to the result Theta join (only = operator)

29 Joins tutors tutor departmentid Koppányi Zoltán FMT Lovas Tamás FMT Tuchband Tamás AGT Gipsz Jakab NULL departments departmentid departmentname FMT Photogrammetry AGT Surveying OCT Chemistry

30 NATURAL JOIN SELECT * FROM tutors NATURAL JOIN departments; tutor departmentid departmentname Koppányi Zoltán FMT Photogrammetry Lovas Tamás FMT Photogrammetry Tuchband Tamás AGT Surveying

31 INNER JOIN SELECT * FROM tutors INNER JOIN departments ON tutors.departmentid = departments.departmentid; tutors.tutor tutors.depart mentid departments. departments. departmentid departmentna me Koppányi Zoltán FMT FMT Photogrammetr y Lovas Tamás FMT FMT Photogrammetr ya Tuchband Tamás AGT AGT Surveying

32 Joins Dangling tuples: a row that that fail to match any row of the other relation in the common attributes. Outer Joins Dangling tuples are returned as well FULL OUTER JOIN LEFT OUTER JOIN, RIGHT OUTER JOIN

33 LEFT OUTER SELECT * FROM tutors LEFT OUTER JOIN departments ON tutors.departmentid = departments.departmentid; tutors.tutor tutors.departm entid departments.de departments.de partmentid partmentname Koppányi Zoltán FMT FMT Photogrammetry Lovas Tamás FMT FMT Photogrammetry Tuchband Tamás AGT AGT Surveying Gipsz Jakab NULL NULL NULL

34 RIGHT OUTER SELECT * FROM tutors RIGHT OUTER JOIN departments ON tutors.departmentid = departments.departmentid; tutors.tutor tutors.departm entid departments.de departments.de partmentid partmentname Koppányi Zoltán FMT FMT Photogrammetry Lovas Tamás FMT FMT Photogrammetry Tuchband Tamás AGT AGT Surveying NULL NULL OCT Chemistry

35 Keeping consistency Update to NULL value Cascaded update CREATE TABLE tablename (, ON DELETE SET NULL ON UPDATE CASCADE );

36 Restrictions For attributes CREATE TABLE students ( neptun VARCHAR(6) NOT NULL, average FLOAT CHECK (average > 0), gender CHAR(1) CHECK (gender IN ('F','M')),... );

37 Restrictions For value range PostgreSQL example! CREATE DOMAIN identifiers INT CHECK (VALUE >= 10000); CREATE TABLE students ( ID identifiers, );

38 Restrictions For records CREATE TABLE students ( name CHAR(30) UNIQUE, name CHAR(1) CHECK (gender = 'F' OR gender = 'M') );

39 Restrictions Creation... name CHAR(30) CONSTRAINT key_name PRIMARY KEY... CREATE DOMAIN salary INT CONSTRAINT highnumber CHECK (VALUE >= ); Modifying ALTER TABLE actors DROP CONSTRAINT key_name; ALTER TABLE directors ADD CONSTRAINT highnumber;

40 References Wikipedia _ddl_dml_and_dcl_commands Jeffrey D. Ullman - Jennifer Widom: A First Course in Database Systems

41 Thank You! Database Systems

SQL language. Jaroslav Porubän, Miroslav Biňas, Milan Nosáľ (c)

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