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OracleTable of contents

• What is a database?• Fundamentals of database• Table management• Inserting data• Updating data• Deleting data• Query management

– Simple queries– Aggregate functions– String manipulation– Date manipulation– Sub queries– Equi join– Outer join– Self join– Union, intersection, minus

• View management• Sequence Management• Index Management• Constraints Management• Triggers• Stored procedures• Exceptions• Sequences• Constraints• DBA features

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Fundamentals of database• Applications are used by end users and they enter a

group of raw data• This data is later collated and used by management to

arrive at meaningful information• Before we first understand the technical aspects of

database, we must understand the business data clearly• Rule 1: In any application, first identify raw data• Rule 2: Group related data and associate data type and

size (summary and detail)• Rule 3: Create a set of samples for each of these groups

for better clarity• Rule 4: Identify unique and non-unique data• Rule 5: Identify the relationship between the data

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Raw Data and Grouping• Let us take railways reservation as the application• The raw data could be

– Passenger name– Age– Date of journey– Train name– From station– To Station– PNR number– Route codes– Stations covered in the route

• The data groups would be• Train related data – train number, train name, route in which it is

running• Station related data – station code, station name, station RMS

Pincode, station type (junction, station etc)• Ticket related data – PNR Number, passenger name, date of

journey, set or berth, age, from station, to station, train code etc

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Unique and non-unique data• Unique data means a data that does not repeat

itself• Station code is unique across country• Train code is unique across country• PNR number is unique across country• Coach number is unique within a train, but not

unique across system• Seat number is unique within a coach and train• Passenger name is not unique• Ticket price is not unique

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Relationship between data• One PNR number is associated with one train

code• One PNR number is associated with one or

more passenger names• One train code is associated with one or more

stations• One train code is associated with one route code• All relationships will fall under one-to-one, one-

to-many, many-to-one• Many-to-many is a combinations of the above• We need to identify the relationships between

the data to understand clearly the dependency between data

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Components of database

• A physical database installation in a machine has the following logical entities– Database (group of tables)

– Tables (that contain data)

– Views

– Index files– Triggers– Sequences– Stored procedures (packages, functions, procedures)

– Users to access the tables

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Table Management• Create, alter and drop are the operations on a table• To create a table, we need to supply the table name, column names

and attributes, for each column whether it is a null or not null column, what is the default value for that column, whether the column is primary key or not

• CREATE TABLE is the command to be used• When we want to add a column to a table or to change the attributes

of a column in a table, we use ALTER TABLE command• We cannot remove a column from a table• If we want to remove the table from the database, we need to use

DROP TABLE command• When a table is dropped, the data is also lost• Dual is a default built-in table to do any on the fly calculations• The usual column data types will be number, varchar2, char, date

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Inserting Data • INSERT operation into a table requires data to

be entered• We can insert all column values or selective

column values• When insert is successful, we will get a success

message• When we try to enter a duplicate value into a

table, we will get duplicate constraint violation message

• During insert, if we do not supply a value, the default value for a column is used to fill up that column

• We can insert data only to one table at a time

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Update Operation• When we want to modify data in a table, we can use

UPDATE command• We can update only one table at a time• When we update we need to use the SET clause to set

the values for a particular column• During update also, if try to update a record, such that it

results in duplicate record, we will get a unique constraint violation message

• If we use update command without WHERE clause, it will update all the records

• It is not recommended to update, without giving a where clause

• Examples– Update employee set salary = 1000– Update employee set salary = 2000 where designation =

‘SALESMANAGER’

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Delete Operation• When we want to remove data in a table, we can

use DELETE command• We can delete only one table at a time• We cannot delete a particular column; it is

always one row or multiple rows• If we use delete command without WHERE

clause, it will delete all the records• It is not recommended to delete, without giving a

where clause• Example

– delete from employee – Delete from employee where designation =

‘HRMANAGER’

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SELECT Queries

• When we want to retrieve data from a table, we use SELECT clause

• Most of the times, testers use SELECT queries only

• SELECT has a lot of variations and clauses. Hence SELECT is a must for all testers

• SELECT queries can handle date and string manipulation commands as well

• SELECT helps to filter, search and sort data• SELECT helps to find out relationships in data

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Simple query

• SELECT * from TRAINS– this will get all columns in the table

• SELECT TRAIN_CODE, TRAIN_NAME from TRAINS – this will return only 2 columns from the table

• SELECT TRAIN_NAME from TRAINS WHERE number_of_coaches > 15– This is a simple filter

• SELECT TRAIN_NAME from TRAINS WHERE number_of_coaches > 15 AND TRAIN_CODE < 100– This is a complex filter

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Aggregate functions• Aggregate functions work on the whole set of

records• SELECT max(salary) from EMPLOYEE

– this will get the maximum salary data from the table• SELECT min(salary) from EMPLOYEE

– this will get the minimum salary data from the table • SELECT avg(salary) from EMPLOYEE

– this will get the average salary data from the table• SELECT count(*) from EMPLOYEE

– this will get the number of records in the table• SELECT sum(salary) from EMPLOYEE

– this will get the sum of all salary data from the table

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String/Numeric/Date Manipulation Functions

• Lower – this will convert to lower case• Upper – this will convert to upper case• Substr – this will return a portion of the string• Soundex – will look for sounding matches• Floor – will show the lower side value• Ceil – will show the upper side value• Round – will round off the number to the nearest value• Sysdate – will show the current date• Current_timestamp – will show the current timestamp• To_date and to_char – to manipulate date formats

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Operators• We can use arithmetic operators like +, -, *, / • Logical operators are AND, OR, NOT• Open and close brackets are used to group

items • % is used along with LIKE operator• Where firstname LIKE ‘%raj%’ will search for raj

anywhere in firstname column• Distinct is an operator on a column to fetch

distinct values present in all rows • IN operator is used to provide a set of values in

the WHERE clause• BETWEEN operator is used to provide a range

of values in the WHERE clause

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SubQuery• Sub query is query within a query• This is used to ensure that the WHERE condition is

further getting values from another query• Select employee_name, salary from employee where

designation = (select designation from positionmaster where positioncategory like ‘%MANAGER%’)

• The innermost select is executed first and then the outer select is executed

• In sub queries, if we use = in where condition, the subquery must return only one value

• In sub queries, if we use IN clause in where condition, the subquery can return more than one values

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JOINs• Joins are nothing but a cross product of one or

more tables• Inner join is used to get records that match a

condition in all tables• In joins we use alias to denote table names• Outer join is used to get records from more than

one tables, irrespective of the condition match in left or right table

• Example– SELECT a.empname, b.projectname from employees

a, projects b where a.employeecode = b.employeecode and b.projectstatus = ‘Active’

• To create outer join we use + sign to the left table or right table

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Union, Intersect, Minus• Union is used to combine many SELECT

queries. The result will be all records fetched by all queries. If 2 records match in 2 different queries, it is printed once in the result

• Intersect is used to combine many SELECT queries. The result will be the common records between the 2 select queries

• Minus is used to find out the difference between 2 SELECT queries

• In all these cases, the columns selected must be the same in all select statements

• We can use all these to find the referential integrity of the database

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Views• A view is a virtual table• A view is used to simplify a complex select

statement• A view can bring multiple data from many tables• For all query purposes, a view is treated as a

table• Create View SalesPeople As Select

employeename from employees where designation like ‘%SALES%’

• When we create views, our job to write complex queries get reduced

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Index Files, Transactions• Index files are pointers to the exact location of a record

on the disk• These help us to search faster. Hence a query executes

faster• If we do not have index on a column, and we search

based on that column, it becomes sequential. The performance will be poor

• Index can be unique or non-unique• By using index files, search works as binary search• When we do insert or update or delete, we can make

that permanent by issuing a COMMIT statement• If we want to ignore the previous insert, update, delete

statements, we use ROLLBACK statement

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Triggers• Trigger is an automatic event that happens based on

insert or update or delete• We cannot pass parameters to triggers• A trigger can happen before or after the operation• Create or replace trigger is used to get the trigger in

database• :NEW.column or :OLD.column is used to retrieve internal

values when the triggers are fired• Drop trigger is used to remove the trigger• To test a trigger, first do the required insert or delete or

update operation on the primary table• Do a select query on the other tables on which the

trigger operated

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Stored Procedures• These are executable code written in PLSQL• These reside inside oracle• We can write loops, conditions etc including exception handling• This comes in 2 parts – package header and package body• The package header contains procedures and function definitions• The package body contains actual executable code of functions and

procedures• Procedures and functions take parameters• They must be explicitly executed and they are not automatic• Before executing procedures, set serveroutput on• Functions must return a value to the left hand side• Usually functions are used when there is only one return value or

there is a true/false returns• Inside stored procedures, people write any database queries as

required by application logic• To execute, from the prompt, give

– exec packagename.procedurename(paramaters)

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Exceptions

• Exceptions must be handled inside stored procedures or triggers

• This will ensure that the code does not crash

• When Others is the generic exception• SQLCODE and SQLERRM will hold the error

number and error text• Usually no_data_found and dup_val_on_index

are checked in most of the places

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Cursors

• When a stored procedure needs to retrieve only one record, we use into clause in the select statement

• When the procedure needs to process a record set, we use cursor

• Declare the cursor and provide the select statement• Use OPEN, FETCH and CLOSE commands to access

the cursor• Cursorname%notfound will be set to true if there are no

more records to fetch• Cursorname%count will provide the number of records in

the cursor

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Sequences

• Sequences are used to generate auto increment values

• Use Create sequence command and provide minimum, maximum, start and increment values

• Sequcen.nextval will provide the next sequence number

• This can be used in any insert statements subsequently

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Constraints

• Not Null is a constraint while creating a table

• Primary Key is a constraint

• Foreign Key is a constraint

• Check is a constraint to ensure that a column has only specified values

• Unique index is also a constraing

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DBA Features

• This list gives only the features and not detailed information– Creating database– Creating users

– Providing access rights to users across tables

– Backup and restore– Crash recovery– Replication– Loading of bulk data

– Partitioning of data across disks