Relational Language

8/8/2019 Relational Language

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Structured

QueryLanguage


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Working with DATES

SYSDATE is a date function that returns the

current database server date.

E.g

SELECT sysdate

FROM dual

Where dual is a dummy table

E.g

SELECT 2*2

FROM dual


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Arithmetic Operators

There are four arithmetic operators and theirorder ofprecedence is as follows only:

1. Multiply (*)

2. Division (/)3. Addition (+)

4. Subtraction (-)

E.g

Select ename, salary, salary+100

From emp;


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ConcatenationOperator

It concatenates columns to another columns.

It is represented by two vertical bars (||).

E.g

Select Fname||Lname

From emp;


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Comparison Operators


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It helps in displaying rows based on a range

of values.

E.g

Select Lname,salary Lower Limit Upper Limit

From emp

Where salaryBETWEEN25000 AND 35000

BETWEENCondition


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IN Condition

It campares for values in a specified set of values. TheIN condition is also known as membership condition.

NOT IN is opposite of IN predicate.

E.g

Select ename,sal,empno,deptno

From empWhere ename IN (Ramos,Clark,Pramada,Aruna)

Where ename NOT IN (Ramos,Clark,Pramada,Aruna)


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LIKECondition

LIKE condition is used to perform the wildcard searchof valid search string values. Here % represents any

sequence of zero or more characters. represents any

single character.

E.g

SELECT Lname,hire_date

FROM emp

WHERE hire_date LIKE %95;

It displays the last name and hire_date of all employees

who joined between January 1995 and December 1995.


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Logical Conditions

(AND,OR,NOT)

A logical condition combines the result of two component

conditions to produce a single result based on them or

inverts the result of a single condition.

E.gSELECT empno,lname,job_id

FROM emp

WHERE salary>=10000 ANDjob_id LIKE 9%5

WHERE salary>=10000 ORjob_id LIKE 9%5WHERE job_id NOT LIKE 9%5


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Rules ofprecedence

1. Arithmetic Operators

2. Concatenation Operator

3. Comparison conditions

4. LIKE,IN

5. BETWEEN

6. NOT logical condition

7. AND logical condition

8. ORlogical condition


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CharacterFunctions

Single-row character functions accept character dataas input and can return both character and numericvalues. CharacterFunctions can be divided into :

Case-manipulation function

Character-manipulation functionLOWERconverts alpha character values to

lowercase

UPPER- converts alpha character values to

uppercase

INITCAP converts alpha character values touppercase for the first letter of eachword and all others in lowercase


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CharacterFunctionsE.g

SELECT empno, lname, deptno empno,LOWER(lname)

FROM empWHERE LOWER(lname) = wills

E.g

SELECT empno, LOWER(lname), deptno

FROM emp

WHERE INITCAP(lname) = wills


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Functions

1. AVG SELECT AVG(sell_price) (Average)2. MIN SELECT MIN(bal_due) (Minimum

Balance)

3. COUNT(*) SELECT COUNT(*) (No. of

rows in the table)

4. MAX SELECT MAX(bal_due) (Maximum

Balance)

5. SUM SELECT SUM(sal) (Total salary of allemployees)

6. ABS SELECT ABS(n) (Absolute)


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Functions

7. POWER SELECT POWER(3,2) (Raised)8. ROUND SELECT ROUND(15.19,1) (Round)

9. SQRT SELECT SQRT(25) (Square Root)

10. SUBSTR- SELECT SUBSTR(SECURE,3,4)(Substring)

11. LENGTH SELECT LENGTH(ELEPHANT)(Length of the string)

12. LTRIM SELECT LTRIM(NISHA,N)(Removes characters from the left of char withinitial characters)

13. RTRIM SELECT RTRIM(SUNILA,A)(Returns char removed after the last character not

in the set.)


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Sorting results ORDERBY - sorts the final result rows in ascending or

descending order

GROUP BY - groups rows in an intermediate resultstable where the values in those rows are the same forone or more columns

HAVING - can only be used following GROUP BYand acts as a secondary WHERE clause, returning onlythose groups which meet a specified condition.Itapplies on group functions only.


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ORDERBYClause

It sorts rows with the ORDERBYClause

ASC : Ascending order (by default)

DESC : Descending order

The ORDERBYclause comes last in the SELECTstatement

E.gSELECT lname,job_id,hire_date SELECT lname,job_id,hire_date

FROM emp FROM emp

ORDERBY hire_date ORDERBY hire_date DESC


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ORDERBY Clause

Sorting by multiple columns

E.g

SELECT lname, salary

FROM empORDERBY deptno, salary DESC;


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GROUP BY Clause

The GROUP BY clause is used to group

rows based on distinct values that exists for

specified columns.

E.g

SELECT prod_no, sum(qty_ordered)FROM sales_order

GROUP BY prod_no


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GROU

P BY e.g. count the number of customers with

addresses in each state to which we deliver:

SELECT STATE, COUNT(STATE)

FROM CUSTOMER_V

GROUP BY STATE;


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HAVING Clause

The HAVING clause can be used in conjunctionwith the GROUP BY clause. HAVING imposes a

condition on the group by clause, which further

filters the groups created by the group by clause.

E.g

SELECT prod_no, sum(qty_ordered)

FROM sales_orderORDERBY prod_no

HAVING prod_no = p001 OR prod_no = p004


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Creating Tables

create table

(

[constraint],

[constraint],

);


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Creating Relations in SQL

Creates the Students relation.

Note: the type (domain) of each field is specified,

and enforced by the DBMS whenever tuples are

added or modified.

CREATE TABLE Students

(sid CHAR(20),

name CHAR(20),login CHAR(10),

age INTEGER,

avg FLOAT)


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Best Practices for Data Definitions -

Tables

Naming conventions

Make sure that table names follow a pre-determined naming convention

e.g., every table name starts with tub Keep table names short, precise, self-explanatory, and clean

Avoid spaces and wildcards (e.g., _) in object names

To avoid ambiguities

To easily search for the object in the database by name

Explicitly indicate the table owner

Use the dbo object owner whereverpossible

To avoid ambiguities andpotential coding errors

To avoid scripting bugs in MS tools (DMO, Query Analyzer)

Security reasons

CREATE TABLE PhoneBook(

FirstName VARCHAR(128),

LastName VARCHAR(128),

PhoneNumber VARCHAR(32))


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Explicitly indicate the target filegroup

Important when production databases use more than one filegroup

Specify the filegroup for

Table data (location of datapages), e.g., ON [PRIMARY]

TEXT / NTEXT / IMAGE / XML columns, e.g., TEXTIMAGE_ON [DEFAUL

Talk to yourproduction DB administrator!

Make sure that total column length does not exceed 8060 bytes

SQL 2K gives a warning upon such table creation; error upon 8060+ insert

SQL 2005 handles 8060+ tables with variable length columns

At a price ofperformance impactCREATE TABLE dbo.utbPhoneBook(

FirstName VARCHAR(128),

LastName VARCHAR(128),

PhoneNumber VARCHAR(32))

ON [PRIMARY]

Best Practices for Data Definitions


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Best Practices for Data Definitions -

Columns

Naming convention

Column names should be standardized, self-explanatory

Every table must have a unique identifier

A column with distinct entries

A set of columns that their combined value is unique Number of columns should be kept minimal

Add a fixed set of columns to every table

e.g., InsertTime, UpdateTime, SQLLogin, BitArray

Helps to control, synchronize, and audit data Populate these columns with an UPDATE trigger

Do not use timestamp/rowversion column types

Column types do not contain enough information

These columns may be omitted in performance sensitive tables

Minimize overhead and performance impact


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Example using create

create table CD_MASTER

(

CD_NO number

CONSTRAINTpk_cd PRIMARY KEY,

CD_NAME varchar2(25),

ARTIST varchar2(25),TYPE varchar2(15)

);


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Inserting Datainsert into

(first_column, second_column,

last_column)

values (first_value, second_value, );


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Adding and Deleting Tuples

Can insert a single tuple using:INSERT INTO Students (sid, name, login, age, avg)

VALUES (53688, Smith, smith@ee, 18, 3.2)

Can delete all tuples satisfying some condition(e.g., name = Smith):

DELETE

FROM Students SWHERE S.name = Smith

Powerful variants of these commands are available;more later!


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Example using insertinsert into CD_MASTERvalues (101, Fields of

Gold, Sting, Rock);

insert into CD_MASTERvalues(102,

Supernatural, Santana, Rock);

insert into CD_MASTERvalues (103, Division

Bell, PinkFloyd, Rock);


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Modifying data

update

set =

where ;


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Deleting Data

delete from

where ;


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Altering table definitionsalter table

add | drop | modify

();


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Deleting tables

drop table

[cascade constraints];


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Querying Multiple Relations

What does the following query compute?SELECT S.name, E.cid

FROM Students S, Enrolled E

WHERE S.sid=E.sid AND E.grade='A'

sid cid grade

53831 arnatic101

53831 Reggae203

53650 Topology11253666 History105

Given the following instance ofEnrolled

S.name .cid

Smith Topology112we get:


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Basic Table Level Operations Creation:Using the create command

Populating tables: Entering values into the table

using the insertcommand Modifying data: Modifying data in the tables using

the update command

Deleting data: Deleting data from tables using the

delete command Altering tables:Using the altercommand

Deleting tables: Deleting tables using the dropcommand


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SQL Overview CREATE TABLE ( , )

INSERT INTO ()

VALUES ()

DELETE FROM WHERE

UPDATE

SET =

WHERE

SELECT

FROM

WHERE


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Semantics of a Query

A conceptual evaluation methodfor the previous query:

1. do FROM clause: compute cross-productof Students and

Enrolled

2. do WHERE clause: Check conditions, discard tuples that fail

3. do SELECT clause: Delete unwanted fields

Remember, this is conceptual. Actual evaluation will bemuch more efficient, but must produce the same answers.


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SELECT < attribute list>

FROM

WHERE

is the list of attribute names whose valuesare to be retrieved by the query

is the list of the relation names required to

process the query

is a conditional expression that identifies the

tuples to be retrieved by the query.


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The SELECT Statement

Is used for queries on single or multiple tables. It has the followingclauses:

SELECT - Lists the columns (and expressions involving columns)from base tables or views to be projected into the table that will bethe result of the command

FROM - Identifies the table(s) or view(s) from which columns willbe chosen to appear in the result table, and includes the tables or

views needed to join tables to process the query WHERE - Includes the conditions for row selection within a singletable or view, and the conditions between tables or views for

joining.


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SELECT Example

Find products with standard price less than $275

SELECT PRODUCT_NAME, STANDARD_PRICE

FROM PRODUCT_V

WHERE STANDARD_PRICE < 275

Comparison Operators in SQL


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The SQL Query Language

The most widely used relational querylanguage.

To find all 18 year old students, we can

write:SELECT *

FROM Students S

WHERE S.age=18

To find just names and logins, replace the first line:

SELECT S.name, S.login

sid name login age gpa

53666 Jones jones@cs 18 3.4

53688 Smith smith@ee 18 3.2


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Distinct and * If the user does not want to see duplicate rows in the result,

SELECT DISTINCT can be used, so SELECT DISTINCT

PRODUCT_NAME would display a results table without

duplicate rows

SELECT * (where * is a wildcard to indicate all columns)

displays all columns from all the tables or views in the

FROM clause


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ORDERBY

e.g. list customer, city and state for all customers in theCUSTOMERview whose address is in Florida, Texas, CaliforniaorHawaii. List the customers alphabetically by state, andalphabetically by customer within each state: i.e. sort the resultsfirst by STATE, and within a state by CUSTOMER_NAME:

SELECT CUSTOMER_NAME, CITY, STATE

FROM CUSTOMER_V

WHERE STATE IN (FL, TX, CA, HI)

ORDERBY STATE, CU

STOMER_NAME;


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GROU

P BY It is also possible to nest groups within groups, the same

logic is used as when sorting multiple items

e.g. count the number of customers with addresses in eachcity to which we deliver. List the cities by state:

SELECT STATE, CITY, COUNT(CITY)

FROM CUSTOMER_V

GROU

P BY STATE, CITY; In general, each column referenced in the SELECT

statement must be referenced in the GROUP BY clause,

unless the column is an argument for an aggregate function

included in the SELECT clause.


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SQL statement

processing order


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Creating and Managing

Database Tables

Naming conventions for tables and columns

Must begin with a letter

Between one and 128 characters Alphanumeric characters

Symbols

Special characters like @, #, $, _

Place the table or field name in square brackets if

The name begins with a character or symbol

Name contains a reserved word

Good idea: avoid special characters, reserved words

and symbols (except for _)


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Creating Database Tables

Specify target database before creatingtables

Three ways to specify target database Select the target database in the Object

Explorer

Select the target database in the database list on

the Management Studio toolbar Execute the T-SQL USE command

USE DatabaseName


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Specify target database before creatingtables

Three ways to specify target database Select the target database in the Object

Explorer

Select the target database in the database list on

the Management Studio toolbar Execute the T-SQL USE command

USE DatabaseName


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Open the Query Editor window

Type the SQL commands in Query Editor

To specify target database To create the table

Execute the query

Command(s) completed successfullymessage should appear in the Messagespane

Save the query file with .sql extension


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Using wildcards

Wildcards can also be used in the WHERE clause if an

exact match is not possible

Here the keyword LIKE is paired with wildcard characters

and usually a string containing the characters that are

known to be the desired matches

The wildcard character % is used to represent any

collection of characters

e.g. using LIKE %DESK when searching

PRODUCT_DESCRIPTION will find all the different

kinds of desks.


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Using wildcards

The underscore ,_, is used to represent exactlyonce character

So using LIKE _-drawer when searching

PRODUCT_NAME will find any products with

specified drawers, such as 3-drawer, 5-draweretc.


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Assignment

1. Draw the concerned E-Rdiagram for it:

University Schema

STUDENT(studno,name,hons,tutor,year)

ENROL(studno,courseno,labmark,exammark)

COURSE(courseno,subject,equip)

STAFF(lecturer,roomno,appraiser)

TEACH(courseno,lecturer)

YEAR(yearno,yeartutor)


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Assignment 2


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A i 3


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Assignment 3

S i lb e r s c h a t z , K o r t h a n d S u d a r s h a n

M o d i f i c a t i o n s & a d d i t i o n s b y S B i r d 2 . 2 1

4 3 3 - 3 5 1 , 2 0 0 3

D a t a b a s e S y s t e m s

E x e r c i s eE x e r c i s e

M o v i e s S t a r s

S t u d i o s

t i t l e

y e a r

n a m e

a d d r e s s

n a m e a d d r e s s

??

Q: What relationship or relationship set can be drawn among these

entities? Label the attributes (if u find any appropirate for thatrelationship) also. Write the Schema for it. Specifying the Keys

related to it (if any).


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Sample Movie Database

M

ovies

Studios

Stars

Owns

Stars-in

title year

lengthfilmType

name address

address

name

street city zip


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Banking Example

branch (branch-name, branch-city, assets)

customer (customer-name, customer-street,customer-only)

account (account-number, branch-name,balance)

loan (loan-number, branch-name, amount)

depositor (customer-name, account-number)

borrower (customer-name, loan-number)


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Example Queries

Find all loans of over $1200

Find the loan number for each loan of an amount greater than

$1200

Wamount> 1200(loan)

loan-number(Wamount> 1200(loan))


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Example Queries Find the names of all customers who have a loan,

an account, or both, from the bank

Find the names of all customers who have a loan and an

account at bank.

customer-name (borrower)customer-name (depositor)

customer-name (borrower)customer-name (depositor)


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Example Queries Find the names of all customers who have a loan at thePerryridge branch.

Find the names of all customers who have a loan at thePerryridge branch but do not have an account at any branch ofthe bank.

customer-name (Wbranch-name = Perryridge

(Wborrower.loan-number = loan.loan-number(borrower x loan ))) customer-name(depositor)

customer-name (Wbranch-name=Perryridge (Wborrower.loan-number = loan.loan-number(borrower x loan)))


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Example Queries Find the names of all customers who have a loan at thePerryridge branch.

Query 2

customer-name(Wloan.loan-number = borrower.loan-number(

(Wbranch-name = Perryridge(loan)) x borrower))

Query 1

customer-name(Wbranch-name = Perryridge (

Wborrower.loan-number = loan.loan-number(borrower x loan)))


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Example Queries

Find the largest account balance

Rename accountrelation as d

The query is:

balance(account) - account.balance

(Waccount.balance < d.balance (account xVd(account)))


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Documents

Relational Language