rdbms_day 3

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RDBMS-Day3 SQL

–Basic DDL statements–DML statements–Aggregate functions

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ER/CORP/CRS/DB07/003

Version No: 2.02Copyright © 2004,

Infosys Technologies Ltd

SQL

SQL is a language that all commercial RDBMS implementations understand.

SQL is a non-procedural language

We would be discussing SQL with respect to oracle syntax

You can’t write programs like the ones you would have done using C langauge

You can only write questions in English like language called queries which will fetch some data rows from the database.

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Data types

IntegerFloatCharVarchar2Numberdate

SQL supports various data types

Integers

Decimal numbers--- NUMBER, INTEGER .

Number is an oracle data type. Integer is an ANSI data type. Integer is equivalent of NUMBER(38)

The syntax for NUMBER is NUMBER(P,S) p is the precision and s is the scale. P can range from 1 to 38 and s from -84 to 127

Floating point numbers---- FLOAT

Fixed length character strings---- CHAR (len)

Fixed length character data of length len bytes. This should be used for fixed length data.

Variable length character strings --- Varchar2(len)

Variable length character string having maximum length len bytes. We must specify the size

Dates-----DATE

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Constants/Literals

ANSI standard defines format for literals

Numeric: 21, -32, $0.75,1.2E4

String: enclosed within ‘ …’

Date : 12-mar-03*

•Oracle has a built in function called TO_DATE. This can be used to convert dates written in other formats

•E.g TO_DATE(‘Mar 12 2003’, ‘mon dd yyyy’)

•The built in function sysdate can be used to obtain the current system date.

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Operators

Arithmetic operators like +,-,*,/Logical operators: AND, ORRelational operators: =,<=,>=, < >

The Arithmetic operators are used to calculate something like given in the example below:

Select * from employee where sal * 1.1 > 1000 ;

The logival operators are used to combine conditions like:

Select * from employee where (sal > 1000 AND age > 25);

The above two examples also illustrate use of relational operators

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NULL

Missing/unknown/inapplicable data represented as a null valueNULL is not a data value. It is just an indicator that the value is unknown

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Statements

DDLDMLDCL

SQL has three flavours of statements. The DDL, DML and DCL.DDL is Data Definition Language statements. Some ex amples:CREATE - to create objects in the database ALTER - alters the structure of the database DROP - delete objects from the database TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed COMMENT - add comments to the data dictionary GRANT - gives user's access privileges to database REVOKE - withdraw access privileges given with the GRANT command DML is Data Manipulation Language statements. Some examples:SELECT - retrieve data from the a database INSERT - insert data into a table UPDATE - updates existing data within a table DELETE - deletes all records from a table, the space for the records remain CALL - call a PL/SQL or Java subprogram EXPLAIN PLAN - explain access path to data LOCK TABLE - control concurrency DCL is Data Control Language statements. Some examp les:COMMIT - save work done SAVEPOINT - identify a point in a transaction to which you can later roll back ROLLBACK - restore database to original since the last COMMIT SET TRANSACTION - Change transaction options like what rollback segment to use

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SQL-DDL

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Example:Example:

CREATE TABLECREATE TABLE Emp (Emp (

EmpNoEmpNo short short CONSTRAINTCONSTRAINT PKeyPKey PRIMARY KEYPRIMARY KEY ,,

ENameEName VarCharVarChar (15),(15),

Job Job CharChar (10) (10) CONSTRAINTCONSTRAINT Unik1 Unik1 UNIQUEUNIQUE,,

Mgr Mgr short short CONSTRAINTCONSTRAINT FKey1 FKey1 REFERENCESREFERENCES EMP (EMP (EmpNoEmpNo),),

HiredateHiredate DateDate ,,

Sal Sal singlesingle ,,

Comm Comm singlesingle ,,

DeptNoDeptNo short short CONSTRAINTCONSTRAINT FKey2 FKey2 REFERENCESREFERENCES DEPT(DeptNoDEPT(DeptNo));));

SQL - CREATE TABLE

Syntax:

CREATE TABLE tablename (column_name data_ type constraints, …)

Used to create a table by defining its structure, the data type and name of the various columns, the relationships with columns of other tables etc.

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ALTER TABLEALTER TABLE EMP (ADDADD Grade short);

ALTER TABLEALTER TABLE EMP (DROPDROP Grade);

SQL - ALTER TABLE

Add/Drop Column

Syntax:

ALTER TABLE tablename (ADD/DROP column_name)

Used to modify the structure of a table by adding and removing columns

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ALTER TABLEALTER TABLE EMP ADD CONSTRAINTADD CONSTRAINT Pkey1 PRIMARY KEYPRIMARY KEY (EmpNo);

ALTER TABLEALTER TABLE EMP DROPDROP CONSTRAINTCONSTRAINT Pkey1;

SQL - ALTER TABLE

Add/Drop Primary key

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ALTER TABLEALTER TABLE EMP ADD CONSTRAINTADD CONSTRAINT Fkey1 FOREIGN KEYFOREIGN KEY (Mgr) REFERENCESREFERENCES EMP (EName);

ALTER TABLEALTER TABLE EMP DROPDROP CONSTRAINTCONSTRAINT Fkey1;

SQL - ALTER TABLE

Add/Drop Foreign key

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DROP TABLEDROP TABLE EMP;;

SQL - DROP TABLE

DROP TABLE– Deletes table structure– Cannot be recovered– Use with caution

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Exercise

Office

City

Region

Mgr

Target

Sales

Empl-Num

Name

Age

Rep_Office

Title

Hire_Date

Manager

Quota

Sales

Cust_Num

Cust_Name

Cust_Rep

Credit_Limit

OFFICE SALESREP

Mfr_ID

Product_ID

Description

Price

Qty_On_Hand

PRODUCTS

CUSTOMER

Order_Num

Order_Date

Cust

Rep

Mfr

Product

Qty

Amount

ORDERS

Taken by

Has Mgr

Works in

Is For

Placed by

Has rep

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Exercise

Refer to the diagram in the previous slide. The relationships between entities are as follows:

OFFICE (Mgr) -> SALESREP (Empl_Num)

SALESREP(Rep_Office)-> OFFICE ( Office)

SALESREP(Manager)-> SALESREP (Empl_Num)

CUSTOMER(Cust_Rep) -> SALESREP (Empl_Num)

ORDERS (Rep)-> SALESREP (Empl_Num)

ORDERS(Mfr)-> PRODUCTS (Mfr_ID)

ORDERS(product)-> PRODUCTS (Prod_ID)

Note: -> means “refers to “ in this context

Consider the two entities OFFICE and SALESREPThe Mgr column of OFFICE refers to the Empl_Num column of SALESREP and the Rep_Office column of SALESREP refers to the Office column of the OFFICE Table.We will not be able to define either foreign keys in the create statement because, the other table would not have got created yet.We would make use of the alter statement in this context

OFFICECREATE TABLE OFFICE (Office NUMBER, City CHAR(20), Region VARCHAR(10), Mgr NUMBER, Target NUMBER, Sales NUMBER );

SALESREP

CREATE TABLE SALESREP ( Empl_Num NUMBER, Name VARCHAR(15), Age NUMBER,Rep_Office NUMBER, Title VARCHAR(15), Hire_Date DATE,

Manager NUMBER CONSTRAINT FK1 REFERENCES SALESREP (Empl_Num),

Quota NUMBER, Sales NUMBER );

To define the foreign keys:

ALTER TABLE OFFICE(ADD CONSTRAINT FK2 FOREIGN KEY(Mgr) REFERENCES SALESREP (Empl_Num) );

ALTER TABLE SALESREP(ADD CONSTRAINT FK3 FOREIGN KEY(Rep_Office) REFERENCES OFFICE(Office) );

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SQL-DML

Here we will discuss about commands using which data from the tables would be extracted and updated in different ways

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SQL - INSERT INTO

Single-row insert

INSERT INTO INSERT INTO S VALUESVALUES(‘S3’,’SUP3’,’BLORE’,10)

Syntax: INSERT INTO tablename VALUES (value list)

Inserting one row, many columns at a time

INSERT INTOINSERT INTO S (SNO, SNAME) VALUESVALUES ((‘‘S1S1’’, , ‘‘SmithSmith’’););

Inserting many rows, all/some columns at a time.

INSERT INTOINSERT INTO NEW_SUPPLIER (SNO, SNAME)

SELECTSELECT SNO, SNAME

FROMFROM S

WHEREWHERE CITY ININ (‘BLORE’,’MADRAS’)

In the first format, we would pass values for all the columns in exactly the same order in which they appear in the table

When we wish to insert values only for few selected columns. For e.g in a student table, we may know only the name, age etc. but not the marks until the student completes the exam for the course and receives the results. So, we may insert only values for name and age columns in this case. The value of remaining columns will be represented as NULL by default.

Here in this third form , we copy data which is already in another table into this table as such

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Examples:Examples:

UPDATEUPDATE S SETSET CITY = ‘KANPUR’ WHEREWHERE SNO=‘S1’

UPDATEUPDATE EMP SETSET SAL = 1.10 * SAL

SQL - UPDATE

With or without WHERE clause

Syntax:

UPDATE tablename SET column_name =value [ WHERE condition]

The examples are quite self explanatory

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DELETE DELETE FROM FROM SP WHEREWHERE PNO= ‘P1’

DELETE FROMDELETE FROM SP

SQL - DELETE FROM

With or without WHERE clause

Syntax: DELETE FROM tablename WHERE condition

Delete all rows from Shipment table for all part number as P1

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SNO SNAME STATUS CITY

S1 Smith 20 LondonS2 Jones 10 ParisS3 Blake 30 ParisS4 Clark 20 LondonS5 Adams 30 Athens

Supplier table - S

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Product table - P

PNO PNAME COLOR WEIGHT CITY

P1 Nut Red 12 LondonP2 Bolt Green 17 ParisP3 Screw Blue 17 RomeP4 Screw Red 14 LondonP5 Cam Blue 12 ParisP6 Cog Red 19 London

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Shipment table - SP

SNO PNO QTYS1 P1 300S1 P2 200S1 P3 400S1 P4 200S1 P5 100S1 P6 100S2 P1 300S2 P2 400S3 P2 200S4 P2 200S4 P4 300S4 P5 400

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Retrieving columns from a table

To select a particular column:

SELECT ColumnName FROM Tablename

To select set of column names,

SELECT column1, column2,… FROM TableName

To select all columns from a table:

SELECT * FROM TableName

Examples:

Get the names of all the suppliers

SELECTSELECT SNAME FROMFROM S;

Get the names and city of all the suppliersSELECTSELECT SNAME, CITY FROMFROM S

Get full details for all Suppliers in S tableSELECTSELECT * FROMFROM S

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SQL SQL -- ALL, DISTINCTALL, DISTINCT

SELECT ALL SELECT ALL PNamePName FROM PFROM P

Get all part numbers:

Get all distinct part numbers

SELECT DISTINCT SELECT DISTINCT PNamePName FROM PFROM P

Distinct will filter repetitive occurrence of a particular value

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SELECT SELECT COL1,COL2,.........

FROMFROM TABLE NAME

WHEREWHERE < SEARCH CONDITION>

Retrieving a subset of rowsRetrieving a subset of rows

For retrieval of rows based on some condition, the syntax is

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SELECTSELECT SNOFROMFROM SWHEREWHERE CITY = ‘PARIS’

Relational operator

= , < , > , <= , >= , != or < >

Get SNO for all suppliers in Paris

Relational operators

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SELECT SELECT SNOFROM FROM SSWHERE WHERE CITY = CITY = ‘‘PARISPARIS’’ AND AND

STATUS >10STATUS >10

Logical operator: AND, OR, and NOT

Get SNO for all suppliers in Paris and status greater than 10

Logical operators

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Get PNO for parts whose weight is one of 12,16 or 17 ?

SELECTSELECT PNOFROMFROM PWHEREWHERE WEIGHT=16 OROR

WEIGHT =12 OR OR WEIGHT = 17

Using logical operators..

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Get parts whose weight is in the range 16 to 19 (inclusive)

SELECTSELECT *FROMFROM PWHEREWHERE WEIGHT BETWEENBETWEEN 16 ANDAND 19

Retrieval using BETWEEN

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Get list of PNO for parts whose weight is one of 12, 16 or 17

SELECTSELECT PNOFROMFROM PWHEREWHERE WEIGHT ININ (12,16,17)

Retrieval using IN

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Get the list of Supplier numbers in the cities ROME , PARIS ?

SELECTSELECT SNOFROMFROM SWHEREWHERE CITY ININ (‘PARIS’ ,’ROME’)

Retrieval using IN

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SELECTSELECT *FROMFROM PWHEREWHERE PNAME LIKELIKE ‘C*’

Get all details of parts whose name begins with cha racter C

SELECTSELECT *FROMFROM PWHEREWHERE PNAME LIKELIKE ‘C?’

Retrieval using LIKE

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Get PNO for parts whose weight is unknown (Blank or not added).

SELECTSELECT PNOFROM FROM PWHERE WHERE WEIGHT IS NULLIS NULL

SQL - Retrieval using IS NULL

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Get all details of shipments whose quantity is kno wn

SELECTSELECT *FROMFROM SPWHEREWHERE QTY IS NOT NULLIS NOT NULL

SQL SQL -- Retrieval using NOT NULLRetrieval using NOT NULL

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Column titles using AS

SELECTSELECT SNO AS [Supplier Number],CITY AS [Supplier City]FROMFROM S

The name given in the square brackets will appear as title of that column in the final output.

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SELECTSELECT COL1,COL2,.......FROMFROM TABLE_NAME

WHEREWHERE <SEARCHCONDITION>

ORDER BY ORDER BY COL-NAME [DESC][DESC]

• by default the order is ASCENDING

SQL - Sorting your results

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Get SNO and STATUS for suppliers in Paris in desce nding order of status

SELECTSELECT SNO, STATUSFROMFROM S

WHEREWHERE CITY=‘PARIS’

ORDER BY ORDER BY STATUS DESCDESC

Retrieval using ORDER BY

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SELECTSELECT CITY,COLOR,WEIGHTFROMFROM PWHEREWHERE WEIGHT IN (12,17)ORDER BY ORDER BY CITY,COLOR DESCDESC

SELECTSELECT CITY,COLOR,WEIGHTFROMFROM PWHEREWHERE WEIGHT IN (12,17)ORDER BY ORDER BY 1 DESCDESC, 2

Retrieval using ORDER BY

When there are more than one column names specified in the ORDER BY clause, the results are sorted based on the first column within which the rows are sorted on the second column … for example , in the query that’s given above,

ORDER BY city, color desc

Let us say the cities are like chennai, bangalore, pune, hydrabad, calcutta etc. then based on cities, the rows will be sorted as

BangaloreCalcuttaChennaiHydrabad etc.Let us say there are 5 rows with bangalore as city and 56 rows with Calcutta as city …Within these 5 rows, they will be arranged based on the color in descending order as say for e.g.

YellowRedGreenBlue

So the display may look something like

Bangalore Yellow 87.6Bangalore Red 45.8Bangalore Green 32.6Bangalore Blue 54.3Bangalore Blue 43.2

Calcutta Yellow 34.5….

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SELECTSELECT PNO, WEIGHT*1000FROMFROM P

Queries involving calculated values

Get PNO and WEIGHT in grams for all parts

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Get PNO and WEIGHT in grams for all parts

SELECTSELECT PNO AS [Part], WEIGHT*1000 AS[Weight in grams]

FROM FROM P

Queries involving strings

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Aggregate Functions

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SUM( ) , AVG( ) , MAX( ) , MIN( ), COUNT( )

SQL - Aggregate functions

Used when information you want to extract from a table has to do with the data in the entire table taken as a set.

Aggregate functions are used in place of column names in the SELECT statement

The aggregate functions in sql are :

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Get total qty of P2 supplied

SELECT SELECT SUM SUM (QTY)FROMFROM SPWHEREWHERE PNO=‘P2’

Aggregate function - SUM

Adds up the values in the specified columnColumn must be numeric data type Value of the sum must be within the range of that data type

Example:

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Example:

Get average qty of shipment supplied by S1

SELECTSELECT AVGAVG(QTY)FROMFROM SPWHEREWHERE SNO=‘S1’

Aggregate function - AVG

Returns the average of all the values in the specified columnColumn must be numeric data type

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Get maximum qty of shipment supplied by S1

SELECT SELECT MAXMAX(QTY)FROMFROM SPWHERE WHERE SNO =‘S1’

Aggregate function Aggregate function -- MAXMAX

Returns the largest value that occurs in the specified columnColumn need not be numeric type

Example:

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Get minimum qty of shipment supplied by S1

SELECT SELECT MINMIN(QTY) FROMFROM SPWHERE WHERE SNO=‘S1’

Aggregate function - MIN

Returns the smallest value that occurs in the specified columnColumn need not be numeric type

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Get total number of suppliers

SELECTSELECT COUNTCOUNT(*) FROMFROM S

Aggregate function - COUNT

Returns the number of rows in the table

Get number of shipments for P2

SELECTSELECT COUNTCOUNT(Qty)FROMFROM SPWHEREWHERE PNO=‘P2’

Count(*) = No of rowsCount(QTY) = No. of rows that do not have NULL Value

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SELECTSELECT MINMIN(Qty), MAX(QTY)FROMFROM SPWHEREWHERE PNO=‘P2’

Using two or more aggregate functions

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Summary of basic DDL and DML

Create , Alter and Drop are the DDL commands

Update, Insert into, Delete from are the basic DML commands that add or remove data from tables

Select statement in its various flavours is used to retrieve information from the table

Aggregate functions work on all the rows of the table taken as a group (based on some condition optionally)

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Thank You!

rdbms_day 3

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