sql revision sql (sequel) is used on a most dbms systems (e.g. access, oracle, ingress, ibm db2,...

SQL Revision

SQL (sequel) is used on a most DBMS systems (e.g. Access, Oracle, Ingress, IBM DB2, MySQL)

This course uses MySQL as the DBMS

RDBMS Tables

• Database consists of a set of tables• Each table has vertical columns (attributes) and horizontal

rows (tuples or records)• Each row (or record) contains fields, one for each column,

which can contain data values• A heading specifies the name and type of the values for

each of the columns• A table can have 0, 1, or more rows• Only one data value (possibly composite) is held in any

one field• Unless NOT NULL is specified in the heading, NULL

values (i.e. unknown) are allowed

Suppliers Table

• Suppliers Table S, with sample values

Yate30BrownS5

London20BlondeS4

Detroit30BlueS3

Detroit10WhiteS2

London20PinkS1

CITYSTATUSSNAMESNo

SQL Tables (cont.)

• The rows have no particular order unless an order is imposed upon them

• The columns are strictly ordered from left to right (rarely significant – unlike 3GL record structures)

• Base Table : Table with a name that exists in its own right

• View: Table derived from other tables– Looks like another table to the user, but it is generated

at the point of use rather than stored

PRIMARY and FOREIGN KEYS

• A CANDIDATE KEY is one or more attributes the value of which is unique for every row

• A PRIMARY KEY for any table is chosen from one of its candidate keys

• A table may have one and only one primary key• A FOREIGN KEY is an attribute in a table whose

values must exactly match those of a primary key of the same or a different table in order to identify the existence of a relationship between rows

SQL Indexes

• Speed up retrieval at expense of:– space

– time for updates

• They are a stored file, with each entry containing :– data value

– pointer to row containing that value in that field

• Can be created by the user• System can choose whether or not to use it

SQL Data Definition Language (DDL)

• CREATE TABLE– Creates an initially empty Base Table – Data values added by other commands– Any column can contain NULL values for one

or more rows unless NOT NULL is specified in its type

– If a column is a Primary Key it must not contain NULL values

SQL Definition of Supplier/Parts DatabaseCREATE TABLE S( SNo CHAR(5), SNAME CHAR(20), STATUS NUMERIC(5), CITY CHAR(15), PRIMARY KEY (SNo) );

CREATE TABLE P( PNo CHAR(6), PNAME CHAR(20), SIZE CHAR(6), WEIGHT NUMERIC(5,1), CITY CHAR(15), PRIMARY KEY ( PNo) );

CREATE TABLE SP( SNo CHAR(5), PNo CHAR(6), QTY NUMERIC(9),PRIMARY KEY (SNo, PNo),CONSTRAINT SP_P FOREIGN KEY ( SNo) REFERENCES S(SNo),CONSTRAINT SP_S FOREIGN KEY (PNo) REFERENCES P(PNo) );

Example Database: Supplier/Parts

S SP

P

Yate30BrownS5

London20BlondeS4

Detroit30BlueS3

Detroit10WhiteS2

London20PinkS1

CITYSTATUSSNAMESNo

London19BIGCogP6

Detroit12MEDIUMCamP5

London14BIGScrewP4

Rome17MEDIUMScrewP3

Detroit17SMALLBoltP2

London12BIGNutP1

CITYWEIGHTSIZEPNAME PNo

400P5S4

300P4S4

200P2S4

200P2S3

400P2S2

300P1S2

100P6S1

100P5S1

200P4S1

400P3S1

200P2S1

300P1S1

QTYPNoSNo

SQL DDL – Built-in Types• Common types built into SQL

– CHAR(n)– VARCHAR(n)– BIT(n)– NUMERIC(p,q)– DECIMAL(p,q)– INTEGER– SMALLINT– FLOAT(p)– DATE– TIME– TIMESTAMP– INTERVAL

SQL – Keys

• At the end of a CREATE TABLE command, specify the Primary Key for that table and any Foreign Keys e.g.

CREATE TABLE SP( SNo CHAR(5) PNo CHAR(6) QTY NUMERIC(9)PRIMARY KEY (SNo,PNo)CONSTRAINT SP_P FOREIGN KEY ( SNo) REFERENCES S(SNo),CONSTRAINT SP_S FOREIGN KEY (PNo) REFERENCES P(PNo));

SQL DDL (cont)

• Additional Commands• DROP TABLE

– Removes a Base Table from the Database

• ALTER TABLE– Allows changes to a base table

• adding types• adding/removing columns

– Must be followed by an SQL table update commande.g. ALTER TABLE S ADD DISCOUNT SMALLINT;

Suppliers Table extended

Suppliers Table S, with sample values

Yate30BrownS5

London20BlondeS4

Detroit30BlueS3

Detroit10WhiteS2

London20PinkS1

CITYSTATUSSNAMESNo DISCOUNT

SQL DDL - Indexes• CREATE INDEX and DROP INDEX

– Used to create and remove indexes– The only commands that relate to indexes– Creates index on column(s) specified of named base

table– If UNIQUE is specified, no two rows are allowed the

same value for indexed field– e.g. CREATE UNIQUE INDEX IXS ON S (SNo);

CREATE INDEX IXSP ON SP (SNo, PNo);DROP INDEX IXSP;• N.B. Indexes result in extra disc space being used and a

slowing down of updates

SQL – DDL VIEWS

• CREATE VIEW and DROP VIEW

– Allows the creation and removal of views– CREATE VIEW viewname AS sql-dml– DROP viewname– e.g. CREATE VIEW GOODSUPPLIERS AS

SELECT SNo,SNAME,CITY FROM S WHERE STATUS > 15;

– DROP VIEW GOODSUPPLIERS;

View: GOODSUPPLIERS

– N.B. Cannot access STATUS information or information, including existence, of White from this view

YateBrownS5

LondonBlondeS4

DetroitBlueS3

LondonPinkS1CitySNAMESNo

SQL – Data Manipulation Language (DML)

• Four main types of DML statements in SQL• SELECT

– Retrieve part of one or more tables– Most frequently used SQL statement

• UPDATE – Updates the data values in an existing table

• INSERT– One method of putting data values into a table

• DELETE– Remove values from a table

SQL – SELECT

• General form:-

SELECT [ DISTINCT ] fields(s) FROM tables(s) [ WHERE predicate] [ ORDER BY field(s) [ GROUP BY field(s) [ HAVING predicate ] ]

Example Database: Supplier/Parts

S SP

P

Yate30BrownS5

London20BlondeS4

Detroit30BlueS3

Detroit10WhiteS2

London20PinkS1

CITYSTATUSSNAMESNo

London19BIGCogP6

Detroit12MEDIUMCamP5

London14BIGScrewP4

Rome17MEDIUMScrewP3

Detroit17SMALLBoltP2

London12BIGNutP1

CITYWEIGHTSIZEPNAME PNo

400P5S4

300P4S4

200P2S4

200P2S3

400P2S2

300P1S2

100P6S1

100P5S1

200P4S1

400P3S1

200P2S1

300P1S1

QTYPNoSNo

SELECT Examples

• SELECT SNo, STATUS FROM S

• SELECT * FROM S

– Selects all the columns from S, i.e. result is whole table

30S5

20S4

30S3

10S2

20S1

STATUSSNo

SELECT Examples (cont.)

• SELECT SNo , STATUS FROM S WHERE CITY=`Detroit` and STATUS > 20

• Predicate can use any of the following:

– Operators = ,( != or <>), >, >= ,< , <=

– BETWEEN value1 AND value 2

– IN ( list of values )

– IS NULL

– LIKE characterpattern)

• Use AND and OR to combine predicates

• Use NOT to negate predicates

• Use parentheses where necessary

30S3

STATUSSNo


• Ordering of rows displayed• SELECT SNo , STATUS FROM S

ORDER BY STATUS ASC

• Opposite order is given by DESC

30S5

30S3

20S4

20S1

20S2

STATUSSNo

SELECT EXAMPLES (cont.)

• The join process produces one table from more than one other table

• e.g. Get supplier names and quantities for supply of part P1

SELECT SNAME,QTYFROM S,SPWHERE (S.SNo = SP.SNo AND PNo = P1 ) ; 300White

300Pink

QTYSNAME


• e.g. Get supplier number, supplier name , quantities and size for screws

SELECT SNo, SNAME, SIZE, QTYFROM S,SP,PWHERE (S.SNo = SP.SNo AND SP. PNo = P.PNo AND PNAME= `Screw`);

300BIGBlondeS4

200BIGPinkS1

400MEDIUMPinkS1

QTYSIZESNAMESNo

PNo PNAME SIZE WEIGHT CITY PrefSNo

P1 Nut BIG 12 London S1

P2 Bolt SMALL 17 Detroit S3

P3 Screw MEDIUM 17 Rome S1

P4 Screw BIG 14 London S4

P5 Cam MEDIUM 12 Detroit

P6 Cog BIG 19 London S1

Yate30BrownS5

London20BlondeS4

Detroit30BlueS3

Detroit10WhiteS2

London20PinkS1

CITYSTATUSSNAMESNo

P

SAdd a preferred supplier `PrefSNo` to table P

Basic Equi Joins return matched rows

SELECT PNo, PNAME, SIZE, WEIGHT, SNAME, STATUSFROM P,SWHERE (P.PrefSNo = S.SNo);

PNo PNAME SIZE WEIGHT SNAME STATUS

P1 Nut BIG 12 Pink 20

P2 Bolt SMALL 17 Blue 30

P3 Screw MEDIUM 17 Pink 20

P4 Screw BIG 14 Blonde 20

P6 Cog BIG 19 Pink 20

Inner Equi Joins return matched rowsSELECT PNo, PNAME, SIZE, WEIGHT, SNAME, STATUSFROM P NATURAL JOIN S;

Implicit match on common attributes by DBMS using the System Catalogue

Or

SELECT PNo, PNAME, SIZE, WEIGHT, SNAME, STATUSFROM P INNER JOIN SON P.PrefSNo=S.SNo;







Outer Joins return all rows in selected table

SELECT PNo, PNAME, SIZE, WEIGHT, SNAME, STATUS

FROM P LEFT JOIN S

ON P.PrefSNo=S.SNo;






P5 Cam MEDIUM 12


Outer Joins return all rows in selected table

SELECT PNo, PNAME, SIZE, WEIGHT, SNAME, STATUS

FROM P RIGHT JOIN S

ON P.PrefSNo=S.SNo;





White 10



Brown 30

Join Types

TS ITS - ST -Inner Join

R ight O uter JoinLeft O uter Join

S T

Full O uter Join

U)-( TS )( TS I ) -( ST)( TS I U

U)-( TS ) -( ST)( TS I U

UUnion Join

)-( TS ) -( ST


• Aggregate functions– Enhance the power of SELECT

– calculation based on the values in the column

• Main ones are:– COUNT The number of values

– SUM The sum of the values

– AVG The average of the values

– MAX and MIN The largest and smallest of the values

• If argument preceded by DISTINCT, duplicate values are eliminated before applying function

SELECT EXAMPLES(cont.)

• DISTINCT must be specified for COUNT since COUNT(*) is used to count number of rows– e.g. SELECT COUNT(DISTINCT SNo) FROM SP returns 4

– SELECT COUNT(*) FROM SP returns 12

• GROUP BY rearranges the table represented by the FROM Clause into groups– e.g. SELECT SNAME,STATUS

FROM S GROUP BY STATUS

30 Brown

30 Blue

10 White

20 Blonde

20 Pink

STATUS SNAME


• The clauses in the SELECT are then applied to each group– e.g. SELECT PNo, SUM(QTY) FROM SP

GROUP BY PNo;

100P6

500P5

500P4

400P3

1000P2

600P1

SUM(QTY)PNo


• The HAVING clause can be used to select groups that meet a given condition

– e.g. SELECT PNo, SUM(QTY) FROM SP GROUP BY PNo HAVING COUNT(*) > 1;

500P5

500P4

1000P2

600P1

SUM(QTY)PNo

SQL: UPDATE

• Used to update existing information in a table

• General form:UPDATE tableSET field(s) = expression {, expression }[ WHERE predicate ] ;

e.g. Double the status of all London based suppliersUPDATE P SET STATUS = 2 * STATUSWHERE CITY = ` London` ;

SQL: INSERT

• One method for adding new values into a table

• General forms:To insert a row of specific values:-INSERT INTO table [ ( field {, field } ) ]VALUES ( constant {, constant} ) ;

or to insert a copy of the table produced by a SELECT command:-INSERT INTO table [ ( field { ,field } ) ]SELECT … FROM ... WHERE …;

e.g. INSERT INTO P (PNo, CITY, WEIGHT) VALUES (`P7`, `Yate`, 24);

SQL: DELETE

• To remove values from a table

DELETE FROM table[ WHERE predicate ] ;

e.g. DELETE FROM S WHERE SNo = `S1`;

More complex SQL queries

• Because of the power of SQL it is possible to nest queries• 1) The result of any SELECT query is a logical table and

thus a SELECT clause can be used instead of a tablename– e.g. SELECT … FROM

( SELECT … FROM … WHERE …) WHERE … ;

• 2) If the result of a SELECT is a single attribute (column), then this can also behave as a set of values in a nested WHERE section– e.g. SELECT … FROM …

WHERE … IN ( SELECT … FROM … WHERE … )

Supplier

Supplier id Supplier_name Supplier_tel Supplier_add1 Supplier_add2 Supplier_add3 Supplier_add4 Supplier_postcode

F1234 Pricey & Co 01234 45678

LB100 Bulbs R Us 01234 234567

Bulby House Bulb Lane Bulbtown BU1 1LB

LB200 Lightemups 0117 9656345

Brightlights Dimview Lane Dimwitty Darksville BS1 2UP

S1234 Really Pricey Ltd 01 01 234 234

The Palace Expensive st Niceplace Deartown DT1 2XX

W1000 Cheap Trash Plc 0898 111111 The Hut By the Allotments

Near my Nan’s Nowhere Nice NN99 1FUStock_item

Stock_id Stock_description Qty_on_hand Reorder_Qty Reorder_levelSales_price_per_uni

tSupplier_code

A12341 Light Bulbs/B - 100W 165 200 100 0.30 LB100

A12343 Light Bulbs/B - 40W 110 200 100 0.25 LB100

A12351 Light Bulbs/T - 100W 175 200 100 0.25 LB200

A12352 Light Bulbs/T - 60W 250 200 100 0.25 LB200

B123657 Fuse - 25amp 164 200 100 0.75 F1234

WG1200 Food Mixer : Big Sucker 88 5 10 25.00 WG12

WG1250 Food Mixer: Weeny thing 55 30 50 12.00 WG1200

WG6610 TV : SONY :Flash Harry 22 10 15 1550.00 S1234

WG667 TV : SONY :Cheaper thing 22 10 15 550.00 S1234

WG668 TV : SONY :Quite Dear 22 10 15 950.00 S1234

WG669 TV : SONY :Outrageous 22 10 15 3550.00 S1234

WR10000 WIRE : 25 amp 100M ROLL 100 100 50 0.05 W1000

WR10003 WIRE : 125 amp 100M ROLL

100 100 50 2.50 W1000

List all the products that are supplied by the supplier of our most expensive product.

SELECT DISTINCTROW Stock_item.Supplier_code, Supplier.Supplier_name, Stock_item.Stock_id, Stock_item.Stock_description, Stock_item.Sales_price_per_unit

FROM Supplier INNER JOIN Stock_item ON Supplier.Supplier id = Stock_item.Supplier_code

WHERE Stock_item.Supplier_code=(SELECT Supplier_code FROM Stock_itemWHERE Stock_item.Sales_price_per_unit=(SELECT

Max(Sales_price_per_unit)FROM Stock_item))ORDER BY Stock_item.Sales_price_per_unit;

Query Result

Supplier_code Supplier_name Stock_id Stock_description Sales_price_per_unit

S1234 Really Pricey Ltd WG667 TV : SONY :Cheaper thing 550.00

S1234 Really Pricey Ltd WG668 TV : SONY :Quite Dear 950.00

S1234 Really Pricey Ltd WG6610 TV : SONY :Flash Harry 1550.00

S1234 Really Pricey Ltd WG669 TV : SONY :Outrageous 3550.00

Database System

DAT AO BJECT S

+DAT A

Data File

Q UERYPRO CESSO R

DAT ABASEM ANAG ER

FILE M ANAG ER

DDLPRO CESSO R

DM LPRO CESSO R

CAT ALO GM ANAG ER

SYST EMCAT ALO G

DAT AO BJECT S

DBM S

DAT ABASEADM INIST RAT O R

DAT ABASEAPPLICAT IO N

PRO G RAM

DBMS has to deal with things like:•Data Integrity

•Transaction Handling

•Record Locking

•Commit & Rollback

•Before/After Imaging

•Backup and Recovery

•Running Stored Procedures & Triggers

create table EMPLOYEE ( EMP_ID NUMERIC(12) not null, DEPT_ID NUMERIC(8) not null, EMP_SSN CHAR(9) not null, EMP_FIRST_NAME VARCHAR(20) not null, EMP_LAST_NAME VARCHAR(30) not null, EMP_BIRTH_DATE DATE not null, EMP_GENDER CHAR(1) not null, EMP_HIRE_DATE DATE not null, EMP_STREET VARCHAR(80), EMP_CITY VARCHAR(40), EMP_STATE CHAR(2), EMP_ZIP CHAR(5), constraint PK_EMPLOYEE primary key (EMP_ID), constraint AK_EMP_UID2_EMPLOYEE unique (EMP_SSN), constraint AK_EMP_UID3_EMPLOYEE unique (EMP_FIRST_NAME, EMP_LAST_NAME, EMP_BIRTH_DATE, EMP_GENDER), constraint FK_EMPLOYEE_RELATIONS_DEPARTME foreign key (DEPT_ID) references DEPARTMENT (DEPT_ID))

create table EXEMPT_EMPLOYEE ( EMP_ID NUMERIC(12) not null, EMP_MONTHLY_SALARY NUMERIC(8,2) not null, EMP_VACATION_WEEKS SMALLINT not null, constraint PK_EXEMPT_EMPLOYEE primary key (EMP_ID), constraint FK_EXEMPT_E_INHERITAN_EMPLOYEE foreign key (EMP_ID) references EMPLOYEE (EMP_ID))

create table NON_EXEMPT_EMPLOYEE ( EMP_ID NUMERIC(12) not null, UNION_ID NUMERIC(8) not null, EMP_HOURLY_RATE NUMERIC(5,2) not null, EMP_OVERTIME_RATE NUMERIC(5,2) not null, constraint PK_NON_EXEMPT_EMPLOYEE primary key (EMP_ID), constraint FK_NON_EXEM_RELATIONS_UNION foreign key (UNION_ID) references "UNION" (UNION_ID), constraint FK_NON_EXEM_INHERITAN_EMPLOYEE foreign key (EMP_ID) references EMPLOYEE (EMP_ID)

Trigger1 to prevent the same emp_id value appearing in both employee subtype tables

CREATE TRIGGER exempt_employee_checkBEFORE INSERT OR UPDATE OF emp_idON exempt_employeeFOR EACH ROWDECLARE dummy INTEGER := 0;BEGIN IF ( INSERTING OR (UPDATING AND :new.emp_id <> :old.emp_id)) THEN SELECT COUNT(*) INTO dummy FROM nonexempt_employee WHERE emp_id = :new.emp_id IF (dummy <> 0) THEN RAISE DUP_VAL_ON_INDEX; END IF; END IF;END;

Trigger2 to prevent the same emp_id value appearing in both employee subtype tables

CREATE TRIGGER non_exempt_employee_checkBEFORE INSERT OR UPDATE OF emp_idON non_exempt_employeeFOR EACH ROWDECLARE dummy INTEGER := 0;BEGIN IF ( INSERTING OR (UPDATING AND :new.emp_id <> :old.emp_id)) THEN SELECT COUNT(*) INTO dummy FROM exempt_employee WHERE emp_id = :new.emp_id IF (dummy <> 0) THEN RAISE DUP_VAL_ON_INDEX; END IF; END IF;END;

MySQL Doesn’t Support:

• Views

• Subselects

• Triggers

• Multi-Table Transaction Control

• See Chris’ paper for MySQL limitations and an overview of SQL1-SQL4 features

sql revision sql (sequel) is used on a most dbms systems (e.g. access, oracle, ingress, ibm db2,...

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