database systems basic sql

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Database Systems

Basic SQL

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Outline

SQL Data Definition and Data Types

Specifying Constraints in SQL

Basic Retrieval Queries in SQL

INSERT, DELETE, and UPDATE Statements in SQL

Additional Features of SQL

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Basic SQL

SQL language Considered one of the major reasons for the

commercial success of relational databases SQL

Structured Query Language Statements for data definitions, queries, and

updates (both DDL and DML) SQL is not a programming language. SQL commands can be used interactively as a

query language within the DBMS or SQL commands can be embedded within programming languages.

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Types of SQL Commands

Data Definition Language (DDL): Commands that define a database - Create,

Alter, Drop

Data Manipulation Language (DML) Commands that maintain and query a

database.

Each statement in SQL ends with a semicolon

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SQL Concept Relational Concept

Table Relation

Row Tuple

Column Attribute

SQL Concept & Relational Concept Terminology:

Table, row, and column used for relational model terms relation, tuple, and attribute

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The CREATE TABLE Command CREATE statement

Main SQL command for data definition Specify a new relation

Provide name Specify attributes and initial constraints

Base tables (base relations) Relation and its tuples are actually created

and stored as a file by the DBMS

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The CREATE TABLE Command

Can optionally specify schema: CREATE TABLE COMPANY.EMPLOYEE ...or CREATE TABLE EMPLOYEE ...

Create the following relation: Student(SSN, Name, GPA, Age).

SQL> create table Student (2 SSN char(9) not null,3 Name varchar(20),4 GPA number(3,2), 5 Age number(2), 6 primary key (SSN));

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Attribute Data Types char(n) fixed length character string of length n

varchar(n) variable length characters of length up to n

number(n,m) integer and real values of up to n digits

number integer and real values of up to 40 digits

integer(n) integer of up to n digits

intege r integer of up to 40 digits

date yyyy-mm-dd (10 positions)

time typically in the form HH:MM:SS

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Domain Definitions CREATE DOMAIN <name> As <data-type>;

CREATE DOMAIN SSN-TYPE AS CHAR(9);

We can use SSN_TYPE in place of CHAR(9)

This style in writing SQL statements is preferred as it makes it easier to change the data types of attributes.

A domain can also have an optional default specification via default clause. CREATE DOMAIN DNO-DOM AS CHAR(2)

DEFAULT 01;

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Specifying Constraints in SQL

Constraints are rules or regulations imposed on data to ensure their integrity and correctness.

Constraints on individual columns.

Constraints on a table.

Constraints on multiple tables.

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Constraints on Columns (1)

Create table Book(

ISBN char(15) primary key,

Title varchar(50) unique,

Price number(5,2) check (Price>0),

Edition number(2) default 1 check (Edition > 0),

Publisher_name varchar(30) references Publisher(Name));

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Constraints on Individual Columns (2) type values must be of the given type not null no null value can be taken unique

Specifies alternate (secondary) keys Dname VARCHAR(15) UNIQUE;

no identical non-null values primary key

Specifies one or more attributes that make up the primary key of a relation

no null value and no identical values Dnumber INT PRIMARY KEY;

check constraint definition values must satisfy the check condition.

Dnumber INT NOT NULL CHECK (Dnumber > 0 AND Dnumber < 21);

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Constraints on Individual Columns (3)

Syntax for column definition:col_name data_type [default value] [constraints]

Syntax for column constraints:[constraint constraint_name][not] null | check condition |unique | primary key |references table_name [(column)][on delete cascade] [on update cascade]

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Create Table Example (4)

Create table Enrollment(

SSN char(9) references Students,

Crs_no varchar(7) not null,

Section_no number(2) not null,

Grade char,

primary key(SSN,Crs_no,Section_no),

foreign key (Crs_no,Section_no)references Section);

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Giving Names to Constraints

Syntax for table constraints:[constraint constraint_name]check condition |unique (column {, column}) | primary key (column {, column}) |foreign key (column {, column})references table_name[(column{, column)]

CHECK clauses at the end of a CREATE TABLE statement Apply to each tuple individually

CHECK (Dept_create_date <= Mgr_start_date);

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Giving Names to Constraints

Create table Graduate(SSN char(9) primary key,

Name varchar(30),

Address varchar(80),

Degree varchar(8) check (Degree in

{‘Bachelor’, ‘Master’, ‘Ph.D.’}),

GPA number (3,2) not null,

unique (Name, Address),

constraint ic12 check (GPA>=2.0 and (Degree=‘Bachelor’ or GPA>=3.0)));

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Disabling and Enabling a Constraint

Disabling a constraint: alter table Graduate disable constraint

ic12;

Enabling a constraint: alter table Graduate enable constraint

ic12;

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Basic Retrieval Queries in SQL SELECT statement

One basic statement for retrieving information from a database

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The SELECT-FROM-WHERE Basic form of the SELECT statement:

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The SELECT-FROM-WHERE Structure Logical comparison operators

=, <, <=, >, >=, and <>

Projection attributes Attributes whose values are to be retrieved

Selection condition Boolean condition that must be true for any

retrieved tuple

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The SELECT-FROM-WHERE

Find the SSN, Name and GPA of all students whose GPA is higher than 3.8.

Select SSN, Name, GPAFrom StudentsWhere GPA > 3.8;

Select all EMPLOYEE SSNs.SELECT SSNFROM EMPLOYEE;

Select all combinations of Employee SSNs and Department Dname.

SELECT SSN, DNAMEFROM EMPLOYEE, DEPARTMENT;

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The SELECT-FROM-WHERE

Select all attributes of employees who work for department number 5;

SELECT * FROM EMPLOYEEWHERE DNO = 5;

Find the names and GPAs of all students who take database systems.Select Name, GPAFrom Student, Enrollment, CourseWhere Title = `database systems` and Students.SSN = Enrollment.SSN and Enrollment.Course_no=Courses.Course_no;

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Ambiguous Attribute Names Same name can be used for two (or more)

attributes As long as the attributes are in different

relations Must qualify the attribute name with the

relation name to prevent ambiguityEMPLOYEE(SSN, Name, …., DNo)DEPARTMENT(DNo, Name, …)

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Aliasing, Renaming, and Tuple Variables Aliases or tuple variables

Declare alternative relation names E and S EMPLOYEE AS E(Fn, Mi, Ln, Ssn, Bd, Addr, Sex, Sal, Sssn, Dno)

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Dealing with Aliasing (1)

For each employee retrieve the employee’s first and last name and the first and last name of his or her immediate advisor.

SELECT E.Fname, E.Lname, S.Fname, S.LnameFROM Employee E, Employee SWHERE E.SuperSSN = S.SSN;

We may write Employee AS E

Note that aliases can be used to shorten queries by giving short names to relations.

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Dealing with Aliasing (2)

We may alias attributes as well. Employee(Name, Address, Supervisor, Dept) Q1:

Select NA, Adr, S, Dept FROM EMPLOYEE AS E(NA, Adr, S, D)

Or this Select Name NA, Address adr, Supervisor

S, Dept DFROM EMPLOYEE;

Find the names and GPAs of all students who take database systems. Select Name, GPA

From Student S, Enrollment E, Course C Where Title=`database systems‘ and

S.SSN=E.SSN and E.Course_no=C.Course_no

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Dealing with Aliasing (3)

Find all pairs of students who have the same GPA.

select s1.SSN, s2.SSN from Student s1, Student s2 where s1.GPA=s2.GPA and

s1.SSN<s2.SSN;

Question: Why use “s1.SSN < s2.SSN”?

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Dealing with Aliasing (4)

Find the names of all students whose GPA is higher than Tom's GPA.

select s1.Name from Students s1, Students s2

where s2.Name=‘Tom’ and s1.GPA>s2.GPA;

Question: Is a student qualified if his/her GPA is higher

than some Tom's GPAs but not all Tom's GPAs?

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Renaming SELECT Attributes

SQL allows us to rename SELECT attributes This does not significantly change the results of

a query, but it does allow us to control the headings of the columns displayed on reports

SELECT FNAME AS FN, LNAME AS LNFROM EMPLOYEEWHERE SUPERSSN IS NULL

The same tuples will be selected as for the last query, but now the columns will be labeled FN and LN instead of FNAME and LNAME.

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Unspecified WHERE Clauseand Use of the Asterisk

Missing WHERE clause Indicates no condition on tuple selection

CROSS PRODUCT All possible tuple combinations

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Unspecified WHERE Clauseand Use of the Asterisk (cont’d.)

Specify an asterisk (*) Retrieve all the attribute values of the selected

tuples

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Unspecified Where Clause & Use of Asterisk

To retrieve all attributes of a relation, use the shorthand * To retrieve all the attribute values of the selected tuples, a * is

used, which stands for all the attributes Find all students whose GPA is higher than 3.8. select * from Students where GPA >

3.8;

The where-clause may be absent. Find the Names of all students.

select Name from Students; Select all EMPLOYEE SSNs.

SELECT SSN FROM EMPLOYEE;

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Unspecified Where clause A missing WHERE-clause indicates no condition;

hence, all tuples of the relations in the FROM-clause are selected

This is equivalent to the condition WHERE TRUE

Retrieve the SSN values for all employees.SELECT SSN FROM EMPLOYEE;

If more than one relation is specified in the FROM-clause and there is no join condition, then the CARTESIAN PRODUCT of tuples is selected

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Use of Asterisk Retrieve all the attributes of an employee and the

attributes of the department he/she works in for every employee of the “Research” department.

SELECT * FROM Employee, Department

WHERE Dname = “Research” AND DNO = Dnumber;

Specify (retrieve) the cross product of the Employee and Department relations;

SELECT * FROM Employee, Department;

Select all combinations of Employee SSNs and Department Dname.

SELECT SSN, DNAME FROM EMPLOYEE, DEPARTMENT;

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Tables as Sets in SQL SQL does not automatically eliminate duplicate tuples in query

results Use the keyword DISTINCT in the SELECT clause

Only distinct tuples should remain in the result Find the Names of all students without duplicate rows.

Select distinct Name from Student; Select all can be used to explicitly request that all

duplicate rows are kept. Is the following query an efficient query? select distinct SSN, Name from Student Retrieve the salary for every employee.

duplicates may appearSELECT Salary FROM Employee;

duplicates will be eliminatedSELECT DISTINCT Salary FROM Employee;

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Tables as Sets in SQL (cont’d.) Set operations

UNION, EXCEPT (difference), INTERSECT Corresponding multiset operations: UNION ALL,

EXCEPT ALL, INTERSECT ALL) union removes duplicate rows. union all keeps duplicate rows.

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Substring Pattern Matching and Arithmetic Operators

LIKE comparison operator Used for string pattern matching % replaces an arbitrary number of zero or more

characters underscore (_) replaces a single character

Standard arithmetic operators: Addition (+), subtraction (–), multiplication

(*), and division (/) BETWEEN comparison operator

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Substring Pattern Matching

Find the course numbers and titles of all courses whose title contains “systems”.

select Course_no, Title from Courseswhere Title like `%systems%`;

% matches 0 or more characters.

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Substring Pattern Matching

Find all students whose name starts with M and is six-character long.

select * from Studentswhere Name like `M_ _ _ _

_`;

_ matches exactly one character not like is the opposite of like.

Find all students whose name contains a _. select * from Students where Name like `%\_ %`;

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Substring Pattern Matching

Retrieve all employees whose address in Housten, Texas.

SELECT Fname, LnameFROM EmployeeWHERE Address LIKE ’%Houston, TX%’;

Find all employees who were born during the 1950s.

SELECT Fname, LnameFROM EmployeeWHERE Bdate LIKE ’195_ _ _ _ _’;

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Arithmetic Operators

Show resulting salaries if every employee working on the ‘productX’ project is given a 10% raise.

SELECT Fname, Lname, 1.1*SalaryFROM Employee, Works_on, ProjectWHERE SSN = ESSN AND PNO = Pnumber AND Pname=“ProductX”;

Find the names of all students whose GPA is between 3.5 and 3.8, inclusive.

select Name from Students where GPA between 3.5 and 3.8;

not between ... and … is the opposite of between … and ...

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Arithmetic Operators

Employees (SSN, Name, Salary) Find the SSN, name and annual salary of each

employee.

select SSN, Name, 12*Salary from Employees;

orselect SSN, Name,12*Salary as Annual_Salary

from Employees;

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Ordering of Query Results Use ORDER BY clause

Keyword DESC to see result in a descending order of values

Keyword ASC to specify ascending order explicitly

ORDER BY D.Dname DESC, E.Lname ASC, E.Fname ASC

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Ordering Tuples

Find the names of all students and order the names in ascending order.

select Name from Studentsorder by Name asc;

ascending order is the default in order by clause.

We can write:order by Dname desc, Lname ASC, Fname ASC

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Ordering Tuples

Find all the students whose GPA is higher than 3.5 and order the result in descending order by GPA, and for students having the same GPA, order them in ascending order by their names.

select * from Students where GPA > 3.5 order by GPA desc, Name asc;

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Ordering Tuples

Retrieve a list of employees and the projects they are working on, ordered by department and, within each department, alphabetically by last name, first name;

SELECT Dname, Lname, Fname, Pname

FROM Department, Employee, Works_on, Project

WHERE Dnumber=DNO AND SSN=ESSN AND PNO=Pnumber

ORDER BY Dname, Lname, Fname;

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Discussion and Summaryof Basic SQL Retrieval Queries

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INSERT, DELETE, and UPDATE Statements in SQL

Three commands used to modify the database: INSERT, DELETE, and UPDATE

Relation schemas under consideration: Student(SSN, Name, GPA, Age) Course(CNo, Title, DName) Enrollment(SSN, CNo, Grade)

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The INSERT Command Specify the relation name and a list of values for

the tuple

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Insert

In its simplest form, it is used to add one or more tuples to a relation

Attribute values should be listed in the same order as the attributes were specified in the CREATE TABLE command.

Syntax: insert into table_name [(column {, column})] [values (expression {, expression})] | [Subselect]

Multiple tuples can be inserted with the same INSERT command, tuples are separated by commas and enclosed between ( and ).

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Insert

Add a new student (123, Ali, null, 22) to the student table Student(SSN, Name, GPA, Age).insert into Students values (`123`,`Ali`,null,22); Order of values should agree with the original

definition of Student. or

insert into student(name, ssn, age) values (`Ali`,`123`,22)

Attributes with NULL and DEFAULT values can be left out.

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Insert

Insert two tuples into the Students tableinsert into Students values (‘111223333’, ‘Smith’, 3.45, 23)

(‘444556666’, ‘Maria’, 3.60, 22);

Suppose table Top_Students (SSN, Name, GPA) has been created.

Find all students whose GPA is 3.8 or higher and save the result in the Top_Students table.insert into Top_Students select SSN, Name,

GPA from Student where GPA >= 3.8;

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Insert

CREATE TABLE DEPTS-INFO(DNAME VARCHAR(15),

NO-OF-EMPS INTEGER, TOTTAL-SAL INTEGER);

INSERT INTO DEPTS-INFO (DNAME, NO-OF-EMPS, TOTAL-SAL) SELECT DNAME, count(*),

sum(SALARY) FROM DEPARTMENT, EMPOYEE

WHERE DNUMBER = DNO GROUP BY DNAME;

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INSERT INTO COURSE(COURSE_CODE, CREDIT_HOURS)VALUES (‘MIS499’,4);

INSERT INTO COURSEVALUES (‘MIS499’,’’,4);

INSERT INTO COURSEVALUES (‘MIS499’,NULL,4);

COLUMN LIST IS NEEDED IF YOU PLAN TO LEAVE OUT A VALUE IN THE VALUE LIST

COLUMN LIST CAN BE OMITTEDIF YOU PUT IN A BLANK VALUE

THE NULL KEYWORD CANBE USED TO CREATE A BLANKCOLUMN

ALL OF THESE ASSUME THAT THE DATABASE ALLOWS THE COLUMN TOBE NULL. YOU CANNOT LEAVE PRIMARY KEYS BLANK

Inserting Null Data

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Delete Removes tuples from a relation Includes a WHERE-clause to select the tuples to be

deleted Tuples are deleted from only one table at a time (unless

CASCADE is specified on a referential integrity constraint)

A missing WHERE-clause specifies that all tuples in the relation are to be deleted; the table then becomes an empty table

The number of tuples deleted depends on the number of tuples in the relation that satisfy the WHERE-clause

Referential integrity should be enforced

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Delete Syntax: delete from table_name [where search_condition]

Delete all tuples from Students. delete from Students;

The schema of Students remains.

Delete all students who take no courses.

delete from Students where SSN not in (select SSN from

Enrollment);

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The DELETE Command Removes tuples from a relation

Includes a WHERE clause to select the tuples to be deleted

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Delete

DELETE FROM Employee WHERE Lname = ‘Brown’;

DELETE FROM Employee where SSN = ‘123456789’

DELETE FROM EMPLOYEE WHERE DNO IN (SELECT Dnumber FROM

Department WHERE Dname = ‘Research’);

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Update

Used to modify attribute values of one or more selected tuples

A WHERE-clause selects the tuples to be modified

An additional SET-clause specifies the attributes to be modified and their new values

Each command modifies tuples in the same relation

Referential integrity should be enforced Syntax:

update table_name set column = {expression | null} {, column = {expression | null}}[where search_condition]

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Update

Increase the GPA of the student with SSN=123 by 0.5.

update Studentset GPA = GPA + 0.5 where SSN = '123';

Set the Grade of every student who takes database systems to be A.

update Enrollment set Grade = 'A' where CNo in (select CNo from Course where title='database systems');

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Update

Change the location and controlling department number of project number 10 to 'Bellaire' and 5, respectively.UPDATE ProjectSET Plocation = ‘Bellaire’, Dnum = 5 WHERE Pnumber=10;

Give all employees in the 'Research' department a 10% raise in salary.UPDATE Employee

SET Salary = Salary * 1.1 WHERE DNO IN (SELECT Dnumber FROM Department WHERE Dname = ‘Research’);

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The UPDATE Command Modify attribute values of one or more selected

tuples Additional SET clause in the UPDATE command

Specifies attributes to be modified and new values