Relational DBMS & SQL. RDBMS, SQL Statements

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1 Relational DBMS & SQL o Data Definition in SQL o Indexes in SQL o Database Queries in SQL o Aggregate Functions of SQL o Special Features of SQL o Database Update in SQL Relational DBMS & SQL 1 RDBMS, SQL Statements 4 Relational DBMS must u Allow to define and manipulate relations u Manage DB in terms of relations u Accept normalized relations 4 SQL ( structured query language ) u ANSI and ISO standard for relational DB u Supported by other non-relational DB systems 4 SQL statements u Data definition: create table, alter table, drop table, create view, drop view, create index, drop index u Data manipulation: select, insert, delete Relational DBMS & SQL 2 Dave McDonald,, GSU 6-1

2 A Relation Example Student Instructor ID s1 s2 s3 s4 s5 Name Jose Alice Tom Sue Steve Age Address Stone Mountain Buck Head Dunwoody Atlanta Stone Mountain GPA Emp# Name Rank Dept e1 e2 e3 e4 Lisa Fred John Abe Professor Ass. Prof. Assc. Prof. Ass. Prof. MATH CSc EE Course Course# Credits Title Intro to Info Systems Intro to Program. w. VB Intermediate Visual Program. Intro to DBMS Analysis/Design Info System Classrooms EMP# SID Course# e1 e3 e2 e2 e3 e4 e2 e1 e1 s1 s3 s2 s1 s1 s4 s2 s3 s Time 12:10 pm 8:00 am 4:30 pm 4:30 pm 8:00 am 7:15 pm 4:30 pm 12:10 pm 12:10 pm Room 100-CS 521-K 327-ALS 327-ALS 521-K 621-G 327-S 100-CS 100-CS Relational DBMS & SQL 3 Create Relations CREATE TABLE TABLE TableName (colname datatype [NOT [NOT NULL] NULL] [UNIQUE] [DEFAULT defaultoption] [CHECK searchcondition] [,...]} [,...]}]] [PRIMARY KEY KEY (listofcolumns),] [UNIQUE (listofcolumns),] [,]] [,]] [FOREIGN KEY KEY (listoffkcolumns) REFERENCES ParentTableName [(listofckcolumns)], [ON [ON UPDATE referentialaction] [ON [ON DELETE referentialaction ]] ]][, ]] [CHECK (searchcondition)] [, ]] [, ]])) BNF Notation: All caps or boldface indicate required reserved words Mixed case or italics indicate user-supplied values Square brackets indicates optional Parentheses are significant. Must be included if shown Bar character ( ) indicates an or condition Relational DBMS & SQL 4 Dave McDonald,, GSU 6-2

3 Create Relations (alternate form) Create Create Table TableTableName (colname datatype [Not [Not Null] Null] [Unique] [Default defaultoption] [Check [ChecksearchCondition] [,...]} [,...]}]] [Primary Key Key (listofcolumns),] [Unique (listofcolumns)] [,,]] [,,]] [Foreign Key Key (listoffkcolumns) References ParentTableName [(listofckcolumns)], [On [On Update referentialaction] [On [On Delete DeletereferentialAction ]] ]][, ]] [Check [Check(searchCondition)] [, ]] [, ]])) BNF Notation: All caps or boldface indicate required reserved words Mixed case or italics indicate user-supplied values Square brackets indicates optional Parentheses are significant. Must be included if shown Bar character ( ) indicates an or condition Relational DBMS & SQL 5 Create Relations (cont d) Create Create table table AUTHORS (AUID (AUID NVARCHAR2(10) NOT NOT NULL, NULL, BOOKNO NVARCHAR2(13) NOT NOT NULL, NULL, AUNAME NVARCHAR2(25), PRIMARY KEY KEY (AUID), (AUID), FOREIGN KEY KEY (BOOKNO) REFERENCES BOOKS ON ON DELETE CASCADE); The NULL value represents a unknown value or is not applicable. Attribute types of Oracle: integer, number( p, q ), char( n ), varchar2(n), nchar(n), nvarchar2(n), date( dd-monthabbrev-yyyy ), long, raw(p), long raw, rowid. DB2 types accepted by Oracle: smallint, decimal(p,q), float, varchar(n), long, varchar A null value can be used for the GPA for a new student Relational DBMS & SQL 6 Dave McDonald,, GSU 6-3

4 CREATE TABLE Creates a table with one or more columns of the specified datatype. With NOT NULL, system rejects any attempt to insert a null in the column. Can specify a DEFAULT value for the column. Primary keys should always be specified as NOT NULL. FOREIGN KEY clause specifies FK along with the referential action Relational DBMS & SQL 7 Alter Relation ALTER TABLE base-relation-name ADD attr-name data-type; DROP TABLE base-relation-name; alter table STUDENT add AptNum char( 5 ); drop table STUDENT; 4 New attribute values in existing tuples are initialized to null values 4 Values for the new attribute must set by the user 4 Only one attribute may be added at a time Relational DBMS & SQL 8 Dave McDonald,, GSU 6-4

5 Indexes o There is no order among tuples All tuples in a relation may be sorted by the primary key attribute values o Indexes speed up data retrieval How many student s tuples would we search for a query with and without indexes? Find all students who live in Atlanta? Index Table AddrIndex Atlanta Boston New York... Ptr Student ID Name Address GPA s1 Joseph Boston 3.7 s2 Alice Atlanta 4.0 s3... Tom... New York Relational DBMS & SQL 9 Create Indexes CREATE [UNIQUE] INDEX index name ON base-relation-name (( attr-name [order], attr-name[order]......)) [CLUSTER]; 4 An index may consist of one or more attributes Example: Address/Age index 4 The Unique option forces unique index tuples The primary key attribute of a relation can be simulated as an indexed attribute with Unique option created by the DBMS. 4 The Cluster option groups index in a physical block 4 An ascending order is by default Relational DBMS & SQL 10 Dave McDonald,, GSU 6-5

6 Drop Indexes create unique index student-id on STUDENT ( ID ASC ) CLUSTER; create index Address-index on Student (Address) create unique index Name-Index on STUDENT ( Name DESC, Age ) CLUSTER; DROP DROP INDEX INDEX index-name; drop drop index indexaddress-index; What are the major advantages and disadvantages of using index? Relational DBMS & SQL 11 Data Retrieval SELECT [[ DISTINCT ]] attribute1 [,attr2, attr3,...] FROM relation1 [, [, relation2, relation3,...] [[ WHERE condition ]] [[ GROUP BY attribute1 [,attr2,...]...]]] [[ Having condition ]] [[ order by by attribute1 [,attr2,...] [ASC DESC] ]] ;; Projection: List List all all student student names names and and addresses. select select Name, Name, Address Address from from STUDENT; Restriction: List List all all student student with with GPA GPA > select select * from from STUDENT where where GPA GPA > 3.0; 3.0; Relational DBMS & SQL 12 Dave McDonald,, GSU 6-6

7 Data Retrieval... Project & Restriction: List all student names and addresses who have GPA > 3.0 and age > 20. select distinct Name, Address from STUDENT where GPA > 3.0 and Age > 20 order by Name DESC 4 SQL does not remove duplicated tuples 4 Distinct requests to remove duplicate tuples 4 Order by sorts the result in ascending or descending order Relational DBMS & SQL 13 Join o Extended Cartesian Product: List all students and classes select from STUDENT.*, CLASSROOMS.* STUDENT, CLASSROOMS o Equijoin: List all students and classes select from where STUDENT.*, CLASSROOMS.* STUDENT S, CLASSROOMS C S.ID = C.SID QUERY: For each student who is taking course from instructor Fred and who has GPA > 3.0 and age > 20, list their names and addresses. Relational DBMS & SQL 14 Dave McDonald,, GSU 6-7

8 Join... o Greater-Than Join: Student ΞAddress > Address Student SQL: o Not-Equal Join: Student ΞAddress <> Address Student SQL: Relational DBMS & SQL 15 Aggregate Functions COUNT (attr) -- --number of of the values in in attr SUM(attr) -- --sum of of the values in in attr AVG (attr) -- --average of of the values in in attr MAX (attr) -- --Maximum value in in attr MIN (attr) -- --Minimum value in in attr List List the the course# course# and and the the total total number number of of students students in in each each course course select select course#, count( count( SID SID )) from from CLASSROOMS group group by bycourse#; List List the the course# course# and and the the total total number number of of students students for for each each course course that that has has less less than than 3 students. select select course#, count count (SID) (SID) from from CLASSROOMS group group by bycourse# Having Having count count (SID) (SID) < 3; 3; Relational DBMS & SQL 16 Dave McDonald,, GSU 6-8

9 Grouping Results Double Grouping List List the the average average GPA GPA of of each each class class and and group group them them by by instructors. select select course#, Emp#, Emp#, sum sum (GPA)/count (STUDENT.ID) from from STUDENT, CLASSROOMS where where STUDENT.ID = CLASSROOMS.SID group group by bycourse#, Emp#; Emp#; 4 Aggregate functions are applied to the query results, not to the result construction Relational DBMS & SQL 17 Retrieval with Like Command '%' any string which n characters, n >= >= 0 '_' '_' any single character. x exact sequence of of string x. x. Result: List all 2000 level courses. select * from COURSE where course# like '2%'; Course# Credit Credit Title Title Intro Intro to to Info. Info. Systems Systems List all introductory courses. select * from COURSE where course# like '%' and Title like 'Intro%'; Relational DBMS & SQL 18 Course# Credit Credit Title Title Intro Intro to to Info Info Systems Systems Intro Intro to to Program. w. w. VB VB Into Into to to DBMS DBMS Dave McDonald,, GSU 6-9

10 Retrieval with Null Values Queries Involve Null Values: List all students who have either unknown address or unknown GPA. select * from STUDENT where Address is null or GPA is null; Relational DBMS & SQL 19 Nested Subqueries SELECT attribute1 [, [, attrib2, attrib3,...]...] FROM relation1 [, [, relation2, relation3,...]...] WHERE attr [not] { in in comparison operator exists } (( query statement(s) ); ); List List names names of of students students who who are are taking taking 2010." 2010." select select Name Name from from STUDENT where where ID ID in in (( select select SID SID from from CLASSROOMS where where course# course# = '2010' ); ); List List names names of of students students who who are are not not taking taking any any courses. courses. select select Name Name from from STUDENT where where ID ID not not in in (( select select SID SID from from CLASSROOMS ); ); Relational DBMS & SQL 20 Dave McDonald,, GSU 6-10

11 Nested Subqueries... QUERY: List all classes taken by student Jose (assuming there is only one student with name Jose). select select * from from CLASSROOMS where where SID SID in in (( select select ID ID from from STUDENT where where Name Name = 'Jose'); 'Jose'); QUERY: For each student who is taking course from instructor Fred and who has GPA > 3.0 and age > 20, list their names and addresses. Relational DBMS & SQL 21 Nested Subqueries... The the condition involving the key word Exist returns a true value if the result of the subquery is not empty. Otherwise, the condition is false. QUERY: List all students who are taking at least one course. select * from STUDENT S where exists ( select * from CLASSROOMS C where C.SID = S.ID); Relational DBMS & SQL 22 Dave McDonald,, GSU 6-11

12 Update Relations UPDATE relation-name SET attr= scalar-expression [[,, attr = scalar-expression ]]... [[ WHERE condition ]];; Give 20% salary raise to those employees whose salary is below 20,000. update EMPLOYEE set salary = salary * 1.2 where salary < 20000; o How many tuples are modified by this single statement? o What should one do if only one tuple should be modified? Relational DBMS & SQL 23 Delete Tuples DELETE FROM relation-name [[ WHERE condition ]] Fire all presidents. delete from where EMPLOYEE title like '%President%'; o How many tuples are removed by this single statement? o What should one do if only one tuple should be removed? Relational DBMS & SQL 24 Dave McDonald,, GSU 6-12

13 Insert New Tuples INSERT INTO relation-name [[(( attr [[,, attr ]]...))]] VALUES (( value [, [, value ]]...));; INSERT INTO relation-name [[(( attr [[,, attr ]]...))]] subquery; insert into STUDENT values ( 's6', 'Peter', 22, 'College Park', 3.8 ); insert into STUDENT ( ID, Age, Name ) values ( 's7', 36, 'Richard' ); insert into S ( s#, Name, c# ) select STUDENT.ID, Name, Course# from STUDENT S, CLASSROOMS C where S.ID = C.SID and GPA > 3.0; Relational DBMS & SQL 25 What is the value of GPA? Query-By-Example (QBE) Data displayed in tabular form Requests made by filling in parts of table Place P. (w. Microsoft, use a check) in all columns to be selected or col. 1 for all Place specified value in column to select matching rows Multiple values on same line implies "AND" condition Multiple values on different lines implies "OR" condition ~ in front of a value implies NOT...e.g. ~RED = NOT RED Use same example (underlined) in same column of two (or more) tables to show a join (w. Microsoft, draw connecting relationship-line from one table to another) Relational DBMS & SQL 26 Dave McDonald,, GSU 6-13