SQL (Full Syllabus Slideshow)

8/8/2019 SQL (Full Syllabus Slideshow)

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Csci455Fall [email protected]

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` SQL standard Data Definitions, Constraints, and Schema Changes inSQL2

Queries in SQL (basic and complex SQLQueries)

Update operations (delete, insert, and updatestatements)

Views (or Virtual Tables ) in SQL Specifying General Constraints as Assertions

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` SQL stands forStructured Query Language

` Developed by IBM

` adopted as standard language for commercial

RDBMS: SQL-86 (orSQL-1) joint effort by ANSI and OSI

SQL-92 (orSQL2)

SQL-99( orSQL3)

x CORE

x OPTIONAL

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A comprehensive non-procedural databaselanguage package that supports standard Supports both DDL and DML

Provides facilities to specify security, authorization, andconstraints

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` SQL uses Table (or relation) Row (or tuple) Column (or attribute)

` Data Definition Commands Create Schema Create tables Create Domain Create view

Alter Table/Schema Drop Table/Schema

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` SQL schema Used to group tables and related constructs

identified by Schema

x Name

x Elements

x tables

x constraints

x view, domains

x

authorization constructs

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` Schema is created using CREATE SCHEMA E.g.,

x CREATE SCHEMA CompanyAUTHORIZATION JSMITH

x JSMITH is the Schema Owner Catalog

x Named collection of schemas

x Information_schema

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` CREATE TABLE used to specify a new relation (or base table)

x CREATE TABLE EMPLOYEE

x

CREATE TABLE COMPANY.EMPLOYEE CREATE VIEW

x Used to create virtual tables

Attributes are ordered

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` CREATE TABLE DEPARTMENT (

DNAME VARCHAR(10) NOT NULL,

DNUMBER INTEGER NOT NULL,

MGRSSN CHAR(9),

MGRSTARTDATE CHAR(9) );

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` Key attributes can be specified via the PRIMARY KEY and UNIQUEphrasesCREATE TABLE DEPT (

DNAME VARCHAR(10)NOT NULL,

DNUMBER INTEGER NOT NULL,

MGRSSN CHAR(9),

MGRSTARTDATE CHAR(9),

PRIMARY KEY (DNUMBER),

UNIQUE (DNAME),

FOREIGN KEY (MGRSSN) REFERENCES EMPLOYEE(SSN));

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Basic Data typesx Numeric

x Integer, Real

x Char string

x Fixed length (CHAR(n))

x Varying length (VARCHAR(n)x bit-string,

x Fixed (BIT(n)) or varying VARYING(n)

x date/time

x Boolean (T,F, Unknown)

x Timestamps (includes both date and time)

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User defined data type

x Domain in SQLx CREATE DOMAIN SSN_TYPEAS CHAR (9);

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` Constraints and default values can be specified oneach attributes

tuple table

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` NULLS can be used as attribute values

` A NOT NULL constraint can be used to specifythat NULL is not permitted

` DEFAULT Value


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` CHECK Clause Used to restrict attribute or domain values

` E.g., To restrict department numbers between integer 1-20 integer

x DNUMBER INT NOT NULL CHECK (DNUMBER>0ANDDNUMBER 0ANDD_NUM


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PRIMARY KEY CLUASE used to specify PK

x E.g., PRIMARY KEY (DNUMBER);

x E.g., Dnumber INT PRIMARY KEY;

FOREIGN KEY CLUASE used to specify FK

x FOREIGN KEY (DNUMBER) REFERENCESDEPARTMENT (DUNMBER)

UNIQUE CLAUSE

x Used for secondary keys

Figure 8.1

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` Update/delete/insertion of tuples may violate referentialintegrity constraints

The default action is Reject the operation

` Schema Designer can specify an alternative action using

referential triggered action clause to any FK constraint Option include

x SET DEFAULT

x SET NULL

x

CASACA

D

E Option must be qualified

x ON DELETE or ON UPDATE

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20

MINT

EMPLOEE

FNAME LNAME SSN BDATE ADDRESS SEX SUPERSSN DNO

DEPT

DEPT_LOC

SNAME DNUM MGRSSNMSDATE

DNUM DLOC

DNO should be Null or

should match a PK of DEPT


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` Names to constraints

Used to identify/modify a particular

constraint Works like CONSTANT declaration inProgram Languages

Figure 8.2

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Used at the end of schema

Applies to individual tuples

Use CHECK for more general constraints

x E.g.,

x CHECK (DEPT_CREATE_DATE < MGRSTARTDATE);

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` THE DROP COMMAND CASCADE

RESTRICT

Used to drop the named schema elements fromdatabase schema

E.g.,

x DROP SCHEMA COMPANY CASCADE

x DROP TABLE DEPENDENT CASCADE

RESTRCITx Used to drop the schema if it has no elements in it

Delete vs. Drop

x Use delete if you want to delete the records but not the tabledefinition

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` Used to change the definition of base table E.g.,

x ALTER TABLE COMPANY.EMPLOYEEADD JOBVARCHAR(12)

x

ALTER TAB

LE COMPANY.EMP

LOYEE

DROPA

DDRE

SSCASCADE;

x ALTER TABLE COMPANY.DEPARTMENTALTER MGRSSNDROP DEFAULT;

x ALTER TABLE COMPANY.DEPARTMENTALTER MGRSSN

SET DEFAULT 344556677x ALTER TABLE COMPANY.EMPLOYEE DROP CONSTRAINT

EMPSUPERFKCASCADE

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` SQL has only one basic statement to retrieveinformation SELECT FROM

WHERE` no relationship to the W operation of relational

algebra` Important features

supports the notion of multi-set (or Bag)

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` General Form: SELECT

FROM

WHERE ;

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` Get the birthday and address of the employee(s)whose name is John B. Smith SELECT BDATE, ADDRESS

FROM EMPLOYEE

WHERE FNAME=JohnAND MINIT =B ANDLNAME = SMITH

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` Get the name and address of allemployee who work for the ResearchDept. SELECT FNAME, LNAME, ADDRESS FROM EMPLOYEE, DEPARTMENT WHERE DNAME=ResearchAND

DNUMBER =DNO

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` For every project located in Stafford, list theproject number, the controlling departmentnumber, and the department managers last

name, address, and birthrate SELECT PNUMBER, DNUM, LNAME, ADDRESS, BDATE FROM PROJECT, DEPARTMENT, EMPLOYEE

WHERE DNUM=DNUMBERAND MGRSSN=SSN

AND PLOCATION = Stafford

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` In SQL, same name can be used For more than one attribute in different tables

used in recursive queries

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` To remove ambiguity, we need to qualify theattributes : use . separator to qualify the attribute

x e.g., suppose LNAME=NAME, and DNO=DNUMBER ,DNAME=NAME

x SELECT FNAME, EMPLOYEE.NAME, ADDRESS

x FROM EMPLOYEE, DEPARTMENT

x WHERE DEPARTMENT.DNUMBER = EMPLOYEE.DNUMBERAND DEPARTMENT.NAME = Research

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` For each employee, find the employees first andlast name and the first and last name of her/hisimmediate supervisor SELECT E.FNAME, E.LNAME, S.FNAME, S.LNAME

FROM EMPLOYEEAS E, EMPLOYEEAS S

WHERE E.SUPERSSN=S.SSN

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E.Fname E.Lname S.Fname S.Lname

J n m Smit Fran lin n

Fran lin n James B r

li ia ela a Jennifer alla e

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` No WHERE-clause means no conditions

` No condition means Cross product operations (v)

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` Get all combinations of EMPLOYEE.SSN andDEPARTMENT.DNAME SELECT SSN, DNAME

FROM EMPLOYEE, DEPARTMENT

` Get all Employee SSN SELECT SSN

FROM EMPLOYEE

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` Use * to get all attributes

` Get all employees working forDept. 5 SELECT *

FROM EMP

LOYEE WHERE DNO=5

` E.g., 2

S

ELECT

*

FROM EMPLOYEE, DEPARTMENT;

WHERE DNO=5 and Dname=Research

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` SQL treats tables as a multi-set (i.e., a set havingduplicates)

` Why?

Duplicate elimination is an expensive operation (sort and

delete) user may be interested in the result of a query

in case of aggregate function, we do not want to eliminateduplicates

` SQLTable with a key is a

SET by definition Why? Because key must be unique

` To treat tables as sets use DISTINCT in SELECTstatement

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Retrieve the salary of every employee,x SELECTALL SALARY

x FROM EMPLOYEE

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Salary

3000

4000

2500

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` Get the salary of every employee USING distinct(set) SELECT DISTINCT SALARY

FROM EMPLOYEE

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Salary

3000

4000

2500

4300

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` NULL represents Value is not known

x e.g., an unknown address

Value is not availablex E.g., unlisted phone number

Value does not applyx E.g., Unmarried employee has no name for his/her spouse

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` Comparisons involving NULL When NULL is involved in comparison, then the result

considered to be unknown Unknown (maybe true or maybe false)

` SQL uses 3-valued logic TRUE, FALSE, UNKNOWN

` How define the SQL evaluate the 3-valued logicalexpressions involving

AND OR NOT


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x y x AND y x OR y Not x

TRUE TRUE TRUE TRUE FALSE

TRUE UNKNOWN UNKNOWN TRUE FALSE

TRUE FALSE FALSE TRUE FALSE

UNKNOWN TRUE UNKNOWN TRUE UNKNOWN

UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN

UNKNOWN FALSE FALSE UNKNOWN UNKNOWN

FALSE TRUE FALSE TRUE TRUE

FALSE UNKNOWN FALSE UNKNOWN TRUE

FALSE FALSE FALSE FALSE TRUE

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` In SELECT-PROJECT-JOIN queries, only thosecombinations of tuples that are evaluated to TRUEare selected


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` Q18: Get the names of all employees who do nothave supervisors SELECT Fname, Lname

FROM EMPLOYEE

WHER Super_ssn IS NULL

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` Complex SQL queries can be formulated using UNION

INTERSECTION

EXECEPT

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` Make a list of Project numbers for projects thatinvolve an employee whose last name is Smith,either as a worker or as a manger of thedepartment that controls the project

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(SELECT DISTINCT PNUMBER FROM PROJECT, DEPARTMENT, EMPLOYEE

WHERE DNUM=DNUMBER AND MGRSSN=SSNANDLNAME=Smith)

UNION

(SELECT DISTINCT PNUMBER FROM WORKS_ON, EMPLOYEE , PROJECT WHERE PNUMBR = PNO AND ESSN=SSN ANDLNAME=Smith)

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` Some queries need the existing values in thedatabase to be retrieved & compared

` Nested queries

used to formulate such queries

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` Make a list of Project numbers for projects thatinvolve an employee whose last name is Smith,eitheras a workeroras a manger of thedepartment that controls the project

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x SELECT DISTINCT PNUMBER

x FROM PROJECTWHERE PNUMBER IN

(SELECT PNUMBERx FROM DEPARTMENT, EMPLOYEE , PROJECT

x WHEREDNUM = DNUMBEANDMGRSSN = SSNAND LNAME = Smith)

x OR

x PNUMBER INx ( SELECT PNO

x

FROM WORKS

_ON, EMPLOYEE

x WHERE ESSN=SSNAND LNAME = Smith);

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` Correlated Queries: When a condition in WHERE clause of a nested query

references attribute(s) of a relation defined in the outerquery

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` Get the name of each employee who has a dependent withthe same first name and the same sex as the employee

` SELECT E.FNAME, E.LNAME

` FROM EMPLOYEEAS E` WHERE E.SSN IN (SELECT ESSN

FROM DEPENDENT

WHERE E.FNAME=DEPENDENT_NAME

AND E.SEX=SEX);

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` A nested query involving = orIN can be replaced bysimple query

SELECT E.FNAME,E.LNAME

FROM EMPLOYEEAS E, DEPEDENTAS D

WHERE E.SSN=D.ESSNAND

E.FNAME=D.DEPENDENT_NAMEAND

E.SEX=D.SEX;

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` Get SSN of all employees who work on the samecombination (project, hours) on some project thatemployee John Smith with SSN=123456789 SELECT DISTINCT ESSN

FROM WORKS_ON WHERE (PNO, HOURS) IN

(SELECT PNO, HOURSFROM WORKS_ONWHERE ESSN=123456789)

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` EXISTS: Checks the result (i.e, SET) of the correlated nested

query to see if it is empty or not

x If the result (i.e., set) is non-empty it returns TRUE

x If the result is empty it returns FALSE

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` Find the name of each employee who has adependent with the same first name and same sexas the employee SELECT E.FNAME, E.LNAME

FROM EMPLOYEE AS E WHERE EXISTS ( SELECT * FROM DEPENDENT WHERE E.SSN=ESSNAND SEX=E.SEX

ANDE.FNAME=DEPENT_NAME)

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` Find the name of each employee who has nodependent SELECT FNAME, LNAME

FROM EMPLOYEE E

WHERE NOT EXISTS

(SELECT *

FROM DEPENDENT

WHERE SSN=ESSN)

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` Retrieve SSNs of all employees who work onproject number 12,22,or33 SELECT DISTINCT ESSN

FROM WORKS_ON

WHERE PNO IN (12,22,33)

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` Join operation can be specified in FROM clause Understandability

UseAS construct to Rename join attributes

Default is inner join

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` Find the name and address of employees whowork in Research department SELECT FNAME, LNAME, ADDRESS

FROM (EMPLOYEE JOIN DEPARTMENT ON

DNO=DNUMBER) WHERE DNAME = Research

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SELECT FNAME, LNAME, ADDRESS

FROM ( EMPLOYEE NATURALJOIN (DEPARTMENTAS DEPT (DNAME, DNO, MSSN, MSDATE)))

WHERE DNAME =Research

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` ALL is comparison operators` Can be used with any other comparison operators

E.g.x v>ALL V

x

where V is a SETx It returns TRUE if v > every element in V

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` get the names of all employees whose salary isgreater than the salary of ALL the employees indepartment 5 SELECT LNAME, FNAME

FROM EMPLOYEE

WHERE SALARY > ALL

x (SELECT SALARY FROM EMPLOYEE WHERE DNO=5);

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` E.g., SELECT E.FNAME, E.LNAME FROM EMPLOYEEAS E WHERE E.SSN

IN (SELECT ESSN FROM DEPENDENT WHERE ESSN=E.SSNAND

E.FNAM=DEPENDENT_NAMEANDSEX=E.SEX

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` Q20:Find the sum of the salaries of all employees in theResearch dept, as well as the max salary, the min salary, andaverage in that dept.

SELECT SUM(SALARY), MAX(SALARY), MIN(SALARY)

AVG(SALARY) FROM (EMPLOYEE NATURALJOIN (DEPARTMENTASDEPT(Dname, Dno, Mssn, Msdate)))

WHERE DNAME=Research

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` GROUP BY CLUASE Used to partition the relation into sub-relation

Works with aggregate functions (e.g. COUNT)

x grouping attribute

x Grouping attribute (s) need to be specified in SELECT clause

x Create separate group for the grouping attribute with NULL values

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` For each department, retrieve the departmentnumber, the number of employees in thedepartment, and their average salary

SELECT

D

NO, COUNT(*), AVG(SALARY) FROM EMPLOYEE

GROUP BY DNO;

x Figure.8.6.(a)

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` Used with GROUP BY clause

` Used as a condition on the sub-relations or groups Groups satisfying the conditions are selected

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` For each project on which more than two employeeswork, get the project number, the project name, thenumber of employees who work on the project SELECT PNUMBER, PNAME, COUNT(*) FROM PROJECT, WORKS_ON WHERE PNUMBER=PNO GROUP BY PNAME, PNUMBER HAVING COUNT(*)>2; Fig.8.6.(b) and (c)

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` Count the totalnumber of employees whosesalaries exceed $40,000 in each department, butonly for department where more than fiveemployees work

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` SELECT DNAME, COUNT (*)

` FROM DEPARTMENT, EMPLOYEE

` WHERE DNUMBER=DNOAND SALARY>40000

` GROUP BY DNAME` HAVING COUNT (*)>5;

` Wrong Selects only department having more than 5 employees

who ALL

make more than 40K

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` SELECT DNUMBER, COUNT (*)

` FROM DEPARTMENT, EMPLOYEE

` WHERE DNUMBER=DNOAND SALARY>4000

AND

D

NO IN (SELECT DNO FROM EMPLOYEE

GROUP BY DNO

HAVING COUNT(*)>5)

GROUP BY DNUMBER

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` The processing steps 1) the WHERE Clause is executed to select individual

tuples

2) HAVING clause executed to select individual groups of

tuples

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` The Insert Command To add a new tuple to employee

x INSERT INTO EMPLOYEE

x VALUES (Richard,K,Marini,653298653,30-dec-52, 98

Oak Forest, Katy, TX,M, 37000,987654321, 4)

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` To enter a new tuple using known attributes INSERT INTO EMPLOYEE (FNAME, LNAME, SSN)

VALUES (Richard, Marini, 653298653);

x the tuple is accepted, if no constraint is violated,

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` INSERT command can be used to load multiple tuplesas the same time Suppose

x CREAT TABLE DEPT_INFOx (DEPT_NAME VARCHAR(15),

NO_OF_EMPS INTEGER,

TOTAL_SAL INTEGER);

INSERT INTO DEPTS_INFO (DEPT_NAME, NO_OF_EMPS,TOTAL_SAL)SELECT DNAME, COUNT(*), SUM (SALARY)FROM (DEPARTMENT JOIN EMPLOYEE ON DNUMBER=DNO)GROUP BY DNAME;

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` Removes tuples from a relation one at a time DELETE FROM EMPLOYEE

WHERE LNAME=Brown

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` One or more tuples can be deleted E.g.. Delete all employees who work for Research dept.

x DELETE FROM EMPLOYEE

x WHERE DNO IN

x (SELECT DNUMBERx FROM DEPARTMENT

x WHERE DNAME=Research);

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` DELETE FROM EMPLOYEE Creates empty table

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` Used to modify values of one (or multiple)selected tuples associated with ONE relation

` E.g.

Change the location and controlling department number ofproject number 10 to Grand Forks and 5

UPDATE PROJECT SET PLOCATION = Grand Forks, DNUM=5 WHERE PNUMBER=10;

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` E.g., Give all employees working in Research department a 10

percent salary raise

x UPDATE EMPLOYEE

xSET SALARY = SALARY *1.1

x WHERE DNO IN ( SELECT DNUMBER

x FROM DEPARTMENT

x WHERE DNAME = Research);

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` Specifying ASSERTIONS/Triggers

` Creating Views

` Writing programs

` Specifying physical

DB

` Granting and revoking privileges

` Specifying Complex Objects

` Concurrency Control/Recovery mechanisms

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` general constraints can be specified as follows CREATE ASSETION SALARY_CONSTRAINT

x CHECK ( NOT EXISTS ( SELECT *

FROM EMPLOYEE AS E, EMPLOYEE

AS M, DEPARTMENTAS DWHERE E.SALARY > M. SALARY

AND E.DNO=D.NUMBERAND

D.MGRSSN=M.SSN));

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` Constraints Prevent the data from being made inconsistent by any

kind of statement

` Triggers

Maintain database consistency and defined operationally

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` A view refers to a single table that is derived from other tables CREAT VIEW WORKS_ON1 ASSELECT FNAME, LNAME, PNAME, HOURS

x FROM EMPLOYEE, PROJECT, WORKS_ON

x WHERE SSN=ESSN AND PNO=PNUMBER

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FNAME LNAME PNAME HOURS

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CREAT VIEW DEPT_INFO(DEPT_NAME, NO_OF_EMPS,TOTAL_SAL)

ASSELECT DNAME, COUNT(*), SUM(SALARY)

x FROM EMPLOYEE, DEPARTMENT

x WHERE DNUMBER=DNO

x GROUP BY DNAME;

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DEPT_NAME TOTAL_SALNO_OF_EMPS

DEPT_INFO


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` SELECT Fname, Lname

` FROM WORKS_ON1

` WHERE Pname =ProjectX;

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` DROP VIEW WORKS_ON1;

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` Used as subroutine mechanism make a complex query easier to understand/reuse

easier to debug

` used as a flexible mechanism foraccess

CONTROL to the data (security)

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` A View is always up to date

` A view is realized at the time we execute a query

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` Two strategies to implement a view Query modification

x Maps the view into the base tables

View materialization

x Create a temporary view tablex Uses incremental approach to keep a materialized table up-

date

x Removes the view table if it is not accessed for certainperiod of time

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` Query on SELECT Fname, Lname FROM WORKS_ON1 WHERE Pname =ProjectX;

` Translated to SELECT Fname, Lname,x FROM EMPLOYEE, PROJECT, WORKS_ON

x WHERE SSN=ESSNAND PNO=PNUMBER

AND Pname =ProjectX;

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` Updating the views can be complicated andambiguous

` an update on a view defined on a single tablewithout any aggregate functions can be mapped toan update on the base table

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SQL (Full Syllabus Slideshow)

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