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CXB 3104

Advanced Database Systems

Lecture 4 SQL, Sub Queries

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SQL Principals

SQL as a data definition language:

allows users to describe the relations and constraints.

SQL as a query language:

declarative - you specify what you want and not how to

retrieve

relationally complete

Updates in SQL:

allows users to insert, delete and modify tables

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SQL Principals - Enhancements

Triggers (SQL:1999)

Programs that respond to events relating to a given

table Stored Procedures(SQL:1999):

Predefined sequences of SQL statements

New data types:

Object-oriented features in SQL:1999, XML in

SQL:2003/2006

Application Programming Interface (API):

ODBC and JDBC provide standard set of DDL/DML

functions

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Deleting Database Components

The drop command allows the removal of

database components, e.g.

DROP TABLE Lecture RESTRICT; Options:

restrict - specifies that the command must not

be carried out if the component being deleted is

not empty.

cascadethe component is removed together

with the components that depend on it.

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Constraints in RDBMS

UNIQUE, NOT NULL, CHECK

Entity integrity - Primary keys

Referential integrity - Foreign keys

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Primary Keys

A primary key is a set of columns that together

makes each row distinct

No two rows will have the same value of this

primary key (implies that no two rows can be

identicalduplicates are disallowed)

Every table must have one primary key

A primary key should not contain a null value

since then it may not be possible to identify

some tuples.

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Intra-relational constraints1

The simplest intra-relational constraints are NOT

NULL, UNIQUE, PRIMARY KEY and CHECK

The first three can be included in a tabledefinition on each column or after the column

definitions

If multiple columns are used to form a composite

PRIMARY KEY, the key definition must be

included in the table definition after the column

definitions.

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Foreign Keys

A FOREIGN KEY is an inter-relational

constraint that references one or more

rows in the table in which it is defined to aprimary key (strictly a candidate key) in another

table.

Every non-NULL value that exists in a foreign

key attribute must also exist in the table for

which it is the primary key. i.e.:

if B references A, A must exist

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Inter-relational constraints-2

If a row of a table with a foreign key is updated or

deleted violations in the referential constraints can

occur.

Four response modes can be given to the foreign key:

cascade, set null, set default, no action, restrict

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Altering a Foreign Key

ALTER TABLE Student DROP PRIMARY KEY

CASCADE;

ALTER TABLE Student DROP CONSTRAINT

stLec CASCADE;

ALTER TABLE Student ADD CONSTRAINT

stLec FOREIGN KEY (roomNo,occurs)

REFERENCES Lecture(roomNo,occurs) ON

DELETE CASCADE;

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Data Manipulation Statements - 1

Data retrieval (Queries)

SELECT custName FROM Customer WHERE

customerCity = Kuala Lumpur; Data storage

INSERT INTO Customer (custName,

customerCity) VALUES (Smith,Penang);

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Data Manipulation Statements - II

Data modification

UPDATE Customer SET customerCity =

Penang, street = Cheras WHEREcustomerName = Smith;

Data removal

DELETE FROM Customer WHERE

customerName = Smith;

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SQL Simple Selects

Find the branch names for each deposit of customers Smith and

Chen that have a balance greater than 200 or less than 100:

SELECT DISTINCT branchName FROM Deposit WHERE

customerName = Smith OR customerName = Chen

AND balance > 200 OR balance < 100;

SELECT DISTINCT branchName FROM Deposit WHERE

balance NOT BETWEEN 100 AND 200 AND

customerName IN (Smith, Chen);

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SQL Union

Find the names of all customers who have either a loan

or an account at the RHB branch:

( SELECT customerName FROM Deposit

WHERE branchName = RHB ) UNION

( SELECT customerName FROM Loan WHERE

branchName = RHB );

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SQL Intersection

Find the names of all customers who have both a loan

and an account at the RHB branch

( SELECT customerName FROM Deposit

WHERE branchName = RHB ) INTERSECT

( SELECT customerName FROM Loan

WHERE branchName = RHB );

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SQL Minus

Return the rows that are in the first table except those

rows that also appear in the second table:

( SELECT customerName FROM Deposit

WHERE branchName = RHB ) MINUS

( SELECT customerName FROM Borrow

WHERE branchName = RHB );

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Multiple Table Queries (Joins)

Can specify multiple tables in the FROM clause to

perform an inner join:

SELECT * FROM Loan, Customer WHERE

Loan.customerName=Customer.customerName;

An alternative way of writing joins:

SELECT * FROM Loan JOIN Customer ON

Loan.customerName =Customer.customerName;

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Inner Join with condition

Specify which column to join and a conditional clause:

SELECT Loan.customerName FROM Loan,

Customer WHERE Loan.customerName =

Customer.customerName AND Loan.amount >

2000 AND Customer.customerCity = Kuala

Lumpur;

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Inner Joinsexample (aliases)

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Outer Joins

Preserve unmatched rows from one or both

tables

LEFT [OUTER] JOIN - preserves unmatchedrows from the left table

RIGHT [OUTER] JOIN - preserves

unmatched rows from the right table

FULL [OUTER] JOIN - preserves unmatched

rows from both tables

Rows that dont match are given NULL values

for columns from the other table

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Left Outer Join - example

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Right outer join

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Full Outer Join

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Single Table Self-Join

Find all the customers who have an account at

same branch at which Patel has an account (also

output the branch names)

SELECT T.customerName FROM

Deposit S, Deposit T WHERE

S.customerName = Patel AND

S.branchName = T.branchName;

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Built-In Functions

Operate on the set of values in a column of a relation and

return a single value. E.g.

SUM([DISTINCT] column-name): sum of values

AVG([DISTINCT] column-name): average value

MIN(column-name): minimum value

MAX(column-name): maximum value

COUNT([DISTINCT] column-name): number of values

excluding NULLS

COUNT(*): number of values in column including NULLS

- where DISTINCT means only include values that are different

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Sub queries: The IN Clause

A sub query is a query that appears in the body of

another expression.

E.g. find the names of a ll customers who have both a

loan and account at the RHB

SELECT customerName FROM Loan

WHERE branchName = RHB AND

customerName IN

(SELECT customerName FROM Deposit

WHERE branchName = RHB);

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Sub queries and Joins

A sub query can sometimes also be expressed as a join.

E.g. find the names of a ll customers who have both a

loan and account at the RHB

SELECT Loan.customerName FROM Loan, Deposit

WHERE Loan.branchName = RHB AND

Deposit.branchName = RHB AND

Loan.customerName = Deposit.customerName;

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Sub queries: The ANY Clause

Find all branches that have greater assets than

at least one branch located in Kuala Lumpur

SELECT branchName

FROM Branch

WHERE assets > ANY

(SELECT assets

FROM Branch

WHERE branchCity = Kuala Lumpur);

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Sub queries: The ALL Clause

Find the names of all branches that have greater assets

than every branches located in Kuala Lumpur

SELECT branchName

FROM Branch

WHERE assets > ALL

(SELECT assets

FROM Branch

WHERE branchCity = Kuala Lumpur);

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Sub queries: The IN Clause

Find all customers who DO NOT have an account at a

branch named RHB:

SELECT S.customerName

FROM Customer S

WHERE customerName NOT IN

(SELECT customerName

FROM Deposit T

WHERE branchName = RHB);

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Sub queries: The EXISTS Clause

Find all customers who DO NOT have an account at a

branch named CIMB:

SELECT S.customerName

FROM Customer S

WHERE NOT EXISTS

(SELECT T.customerName

FROM Deposit T

WHERE branchName = CIMB

AND S.customerName =

T.customerName);

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Insertion using a query

Provide all loan customers in the RHB branch with a $

200 saving account. Let the loan number serve as the

account number for the new savings account

INSERT INTO Deposit

SELECT customerName, branchName,

loanNumber, 200

FROM Loan WHERE branchName = RHB;

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Deletion using a sub query

Delete all accounts at banks located in CIMB

DELETE FROM Deposit

WHERE branchName IN

(SELECT branchName

FROM Branch

WHERE branchCity = CIMB);

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