Database Languages

Database Languages

Part – II

Data Manipulation

Language

Data Manipulation Language

3.5 String matching

Fuzzy matching: NAME LIKE ‘S%’• Select the tuples with name starting with S.

Customer

Cust_No Name Address

C1 Nippers Ltd 25 High St, Leeds

C2 Tots-Gear 5 Low, Oxford

C3 Super-Brat 30 New St Luton

C6 Tiny-Togs 1 Old Rd, Luton

C3 Super-Brat 30 New St Luton


3.5 String matching

% represents an arbitrary string.- represents a single arbitrary character.[] square brackets may contain any number

of letters, each of which is tested individually.

B%; B_OWN; B[RLO]OWN; [N_P]%


3.6 Testing for null values

SELECT *FROM PRODUCTWHERE COLOUR IS NULL

SELECT *FROM PRODUCTWHERE COLOUR = ‘ ’

They are not same!


3.7 Computation

+ add- subtract* multiple/ divide** to the power of

abs absoluteatan arctangentcos cosineexp exponentiallog natural logarith

mmod modulesin sinesqrt square root


3.8 Summarising functions

AVG averageMAX largest value of an attributeMIN minimum value of an attributeSUM total of the values of an attributesCOUNT count the number of value in an

attribute


3.8 Summarising functions

Example: SELECT AVG(QTY) FROM STOCK SELECT COUNT (*) FROM STOCK

WAREHOUSE_NO BIN_NO PRODUCT_NO QTY

WH1 1 P1 300

WH1 2 P2 50

WH2 1 P2 250

STOCK

200

3


3.9 GROUP BY: used to specific groupings of tuples.

SELECT PRODUCT_NO, IN_STOCK = SUM(QTY)FROM STOCKGROUP BY PRODUCT_NO


WH1 1 P1 300

WH1 2 P2 50

WH2 1 P2 250

STOCK

PRODUCT_NO IN_STOCK

P1 300

P2 300


3.9 ORDER BY: on groupings of tuples.

SELECT * FROM PRODUCT ORDER BY COLOURPRODUCT

PRODUCT_NO NAME COLOUR

P1 Pantaloons blue

P7 Socks bule

P4 Socks harebell

P2 Pantaloons khaki

P3 Socks white

PRODUCT


P1 Pantaloons blue

P2 Pantaloons khaki

P3 Socks white

P4 Socks harebell

P7 Socks bule


3.10 Retrieval from two relations

The join operator of relational algebra makes it possible to define a relation which is made up of data taken from more than one relation.


3.10 Equi-join

Combines tuples in two relations when specified attributes have the same value

SELECT PRODUCT.*, ORDER_LINE.*FROM PRODUCT, ORDER_LINEWHERE

PRODUCT.PRODUCT_NO=ORDER_LINE.PRODUCT_NO;


PRODUCT


P1 Pantaloons blue

P2 Pantaloons khaki

P3 Socks white

P4 Socks harebell

P7 Socks bule

ORDER_LINE

ORDER_NO PRODUCT_NO

QUANTITY

01 P1 100

01 P2 20000

01 P6 20

02 P2 1000

02 P6 10000

PRODUCT.PRODUCT_NO

NAME COLOUR ORDER_NO ORDER_LINE.PRODUCT_NO

QUANTITY

P1 Pantaloons blue 01 P1 100

P2 Pantaloons khaki 01 P2 20000

P2 Pantaloons khaki 01 P2 1000


3.11 Correlation Names

Sometimes, you may want to use a shorter name

SELECT P.*, O.*FROM PRODUCT P, ORDER_LINE OWHERE P.PRODUCT_NO = O.PRODUCT_NO;


3.12 Natural join

Combines tuples of relations!SELECT P.*, O.ORDER_NO, QTYFROM PRODUCT P, ORDER_LINE OWHERE P.PRODUCT_NO = O.PRODUCT_NO;

PRODUCT.PRODUCT_NO

NAME COLOUR ORDER_NO QTY

P1 Pantaloons blue 01 100

P2 Pantaloons khaki 01 20000

P2 Pantaloons khaki 01 1000


3.13 Theta-join

SELECT S.*, O.*FROM STOCK_TOTAL S, ORDER_LINE OWHERE S.QUANTITY > O.QUANTITY;

3.14 Outer-join: retain all the tuples (pp.105)

SELECT S.*, O.*FROM STOCK_TOTAL S, ORDER_LINE OWHERE S.PRODUCT_NO = O.PRODUCT_NO (+);


3.15 Example

SELECT O.*FROM PRODUCT P, ORDER_LINE OWHERE P.PRODUCT_NO = O.PRODUCT_NO AND P.NAME = ‘Pantaloons’;PRODUCT


P1 Pantaloons blue

P2 Pantaloons khaki

P3 Socks white

P4 Socks harebell

P7 Socks bule

ORDER_LINE

ORDER_NO PRODUCT_NO

QUANTITY

01 P1 100

01 P2 20000

01 P6 20

02 P2 1000

02 P6 10000


3.16 Comparing Rows

SELECT F.PRODUCT_NO S.PRODUCT_NO, NAMEFROM PRODUCT F, PRODUCT SWHERE F.NAME = S.NAME AND F.PRODUCT_NO > S.PRODUCT_NO;

FPRODUCT_NO

SPRODUCT_NO

SNAME

P2 P1 Pantaloons

P4 P3 Socks

P7 P3 Socks

P9 P3 Socks

P7 P4 Socks

P9 P4 Socks

P9 P7 Socks


3.17 Queries on more than two relations

SELECT P.NAME, COLOURFROM CUSTOMER C, SALES_ORDER S, ORDER_LINE

O, PRODUCT PWHERE CUSTOMER.NAME = ‘Nippers Ltd’ AND C.CUSTOMER_NO = S.CUSTOMER_NO AND S.ORDER_NO = O.ORDER_NO AND S.PRODUCT_NO= P.PRODUCT_NO;


3.18 Nested SELECTsA SELECT statement is included within the WHERE

clause.SELECT P.NAME, COLOURFROM PRODUCT P, ORDER_LINE OWHERE P.PRODUCT_NO=O.PRODUCT_NO AND O.ORDER_NO=’01’SELECT NAME, COLOUR

FROM PRODUCTWHERE PRODUCT_NO IN (SELECT PRODUCT_NO FROM ORDER_LINE WHERE ORDER_NO = ’01’);


3.18.1 Qualified comparisonSELECT target_list_1FROM List_of_relations_1WHERE attribute IN (SELECT target_list_2 FROM list_of_relations_2 WHERE condition);

The inner SELECT retrieves a set of values, and the outer SELECT retrieves tuples where (using IN) specific attribute values are member of that set.


3.18.1 Qualified comparison

SELECT *FROM EmployeeWHERE AGE > ALL (SELECT AGE FROM Employee WHERE

DEPT_NO=‘D1’);

Understand the ALL and ANY!

SELECT *FROM EmployeeWHERE DEPT_NO <> ‘D1’ AND

AGE < ANY (SELECT AGE FROM Employee WHERE DEPT_NO=‘D1’);


3.18.2 Nested SELECT on primary key

=, <, >, !=, <=, >= Could be applied for primary key.SELECT *FROM EmployeeWHERE NAME = (SELECT NAME FROM PRODUCT WHERE PRODUCT_NO=‘P1’);

Primary key


3.19 Changing values in the database

UPDATEDELETEINSERT

UPDATE PRODUCTSET COLOUR = ‘violet’, PRICE = PRICE+0.2WHERE COLOUR =‘blue’;

INSERT INTO PRODUCT (PRODUCT_NO, NAME, PRICE)

VALUES (‘P10’, ‘Shirt’, 4.95);DELETE FROM PRODUCT WHERE COLOUR =

‘blue’;


3.20 Views of database

A virtual relation is a relation that appears to the user to exist, and can be manipulated as if it were a base relation, but which does not actually exist.

It is a relation retrieved from other relations in the database.

A virtual relation is called a View, and SQL include CREATE VIEW and DROP VIEW to create and delete it.




WHI 1 P1 100

WH1 2 P2 50

WH2 1 P2 50

CREATE VIEW WH1_STOCK_AAS SELECT BIN_NO, PRODUCT_NO, QTYFROM STOCKWHERE WAREHOUSE_NO = ‘WH1’;

STOCKBIN_NO PRODUCT_NO QTY

1 P1 100

2 P2 50

WH1_STOCK_A



CREATE VIEW WH1_STOCK_CAS SELECT WAREHOUSE_NO, BIN_NO,

PRODUCT_NO, NAME, QTY FROM STOCK PRODUCT

WHERE STOCK.PRODUCT_NO=PRODUCT.PRODUCT_NO AND WAREHOUSE_NO = ‘WH1’;


3.21 Integrity constraints

Integrity constraints are rules that must be obeyed by all tuples in the database.

CREATE INTEGRITY ON ORDER_LINE IS QUANTITY > 0 AND QUALTITY <= 10000;

Value out of range (0,10000) will be not allowed.

Database Language

3.22 SUMMARY

SQL has two parts:1) SDL: schema definition language2) DML: data manipulation language

Reading:

Exercises

Chapter 3

3.7-3.13

Database Languages

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