The document discusses various SQL commands for retrieving data from Oracle databases. It covers the SELECT statement and its clauses like WHERE, DISTINCT, LIKE, BETWEEN, IN and operators like AND, OR, NOT. It also discusses NULL values, concatenation, character strings, dates and basic SQL terminology. The SELECT statement is used to retrieve data from tables and supports filtering rows and selecting specific columns.

1. PRACTICAL 03
TO BECOME FAMILIAR WITH DATA RETRIEVAL
COMMANDS

2. Oracle Database (Oracle DB)
• Oracle database (Oracle DB) is a relational database
management system (RDBMS) from the Oracle Corporation.
• Oracle DB is also known as Oracle RDBMS and, sometimes, just
Oracle.
• The system is built around a relational database framework in
which database objects may be directly accessed by users (or an
application front end) through structured query language (SQL).

3. • Oracle DB editions are broken down as follows:
• Enterprise Edition: Offers all features, including superior
performance and security, and is the most robust
• Standard Edition: Contains basic functionality for users that do not
require Enterprise Edition’s robust package
• Express Edition (XE): The lightweight, free and limited Windows
and Linux edition.
• Oracle Lite: For mobile devices

4. Structured Query Language (SQL)
• SQL is the ANSI standard language for relational databases. All
operations on the data in an Oracle database are performed using SQL
statements.
• SQL is a declarative language. SQL is nonprocedural and describes what
should be done. Users specify the result that they want (for example, the
names of employees), not how to derive it.
• SQL is used to query, insert, update and modify data.
• A query language, such as Structured Query Language (SQL), is used to
prepare the queries.

5. • SQL statements are used to perform tasks such as insert, update
data on a database, or retrieve/select data from a database.
• SQL statements are case insensitive. (Statements that do not
distinguish between uppercase and lowercase are said to be case-
insensitive.)

6. DATA RETRIEVAL/SELECT COMMANDS
• Data retrieval means obtaining or extracting data from the database management system.
• Select statements are used to retrieve data from SQL tables. OR The SELECT statement
is used to select data from tables.
• Syntax:
SELECT column1, column2, ...
FROM table_name;
 SELECT identifies what columns.
 FROM identifies which table.
EXAMPLE:
SELECT ename from emp;

7. SELECT COMMAND WITH AN ASTERISK (*)
• Use * with select statement to retrieve all the records stored in
the table.
• SYNTAX:
SELECT * from table_name;
• EXAMPLE:
SELECT * from emp;
• It returns all the columns of the emp table.

8. SELECT DISTINCT Statement
• The SELECT DISTINCT statement is used to return only distinct
(different) values.
• Inside a table, a column often contains many duplicate values; and
sometimes you only want to list the different (distinct) values.
• DISTINCT keyword is used to eliminate the duplicate values.
• DISTINCT suppresses duplicates.

9. WHERE CLAUSE
• WHERE clause can be used to limit the number of rows.
• It is used to extract only those records that fulfill a specified condition.
• If the given condition is satisfied, then only it returns a specific value from
the table.
SYNTAX:
SELECT column1, column2, columnN
FROM table_name
WHERE [condition]
EXAMPLE:
1. SELECT ename, job, salary from emp WHERE job='CLERK' ;
2. SELECT ename, job, salary from emp WHERE salary>20000 ;
3. SELECT * FROM Customers WHERE CustomerID=1;

10. Operators in SQL
• An operator is a reserved word or a character used in an SQL
statement's WHERE clause to perform operation(s), such as
comparisons and arithmetic operations.
• These Operators are used to specify conditions in an SQL statement.
• Operators used in SQL are:
– Arithmetic operators
– Comparison operators
– Logical operators

11. SQL Arithmetic Operators
• Assume 'variable a' holds 10 and 'variable b' holds 20, then

12. SQL Comparison Operators
• Assume 'variable a' holds 10 and 'variable b' holds 20, then

13. Continued..

14. SQL Logical Operators

17. LIKE Operator:
• The LIKE operator is used in a WHERE clause to search for a
specified pattern in a column.
• There are two wildcard characters used in conjunction with the
LIKE operator:
% The percent sign represents zero, one, or multiple characters.
_ The underscore represents a single character.
• A wildcard character is used to substitute any other character(s) in
a string.

18. LIKE Syntax

19. EXAMPLE
SELECT * FROM Customers
WHERE CustomerName LIKE 'a%';
 Display all employee names in which the third letter of the name
is a.
• select ename
from emp
where ename like '__a%';
2 underscore represents 2 letters before a and % represents
multiple or zero characters after a.

20. AND, OR and NOT Operators
• The WHERE clause can be combined with AND, OR, and NOT
operators.
• The AND and OR operators are used to filter records based on
more than one condition:
• The AND operator displays a record if all the conditions separated
by AND is TRUE.
• The OR operator displays a record if any of the conditions
separated by OR is TRUE.
• The NOT operator displays a record if the condition(s) is NOT
TRUE.

22. AND Example
SELECT * FROM emp
WHERE job='PROFESSORE' AND sal=20000;
OR Example
SELECT * FROM emp
WHERE job='PROFESSORE' OR job='CLERK' ;
NOT Example
SELECT * FROM emp
WHERE NOT job='CLERK';

23. IN Operator
• The IN operator allows you to specify multiple values in a
WHERE clause.

24. BETWEEN Operator
• The BETWEEN operator selects values within a given range. The
values can be numbers, text, or dates.
• The BETWEEN operator is inclusive: begin and end values are
included.

25. Aliases
• aliases are used to give a table, or a column in a table, a
temporary name.
• Aliases are often used to make column names more readable.
• An alias only exists for the duration of the query.
SELECT ename AS “Employee
Name”, sal AS “salary” FROM
emp ;

26. NULL Value
• A field with a NULL value is a
field with no value or unknown
or unassigned value.
• How to Test for NULL
Values?
• It is not possible to test for
NULL values with comparison
operators, such as =, <, or <>.
• We will have to use the IS
NULL and IS NOT NULL
Null value is not the same as zero
or a blank space.

27. EXAMPLE
– Display the employee name and job title of all the employees
who do not have a manager.
SELECT ename, job, mgr FROM emp
WHERE mgr IS NULL;
Display the employee name and job title of all the employees who
have a manager.
SELECT ename, job, mgr FROM emp
WHERE mgr IS NOT NULL;

28. Concatenation Operator
• Concatenates columns or character strings to other columns.
• It is represented by two vertical bars ||
• EXAMPLE:
– Display the employee name and job as a single output and name the
column “Employees”.
SELECT ename || job AS 'Employees' FROM emp;

29. CHARACTER STRINGS AND DATES
• Character strings and dates are enclosed in single quotation marks.
• Character values are case sensitive, and date values are format
sensitive.
• Default date format is: DD_MON_YYYY
• Eg:
– SELECT ename, job, salary FROM emp
WHERE job='CLERK' ;

30. • Keyword:
– it refers to an individual SQL element.
Eg: SELECT and FROM are Keywords.
• CLAUSE:
– A clause is a part of SQL statement. Clauses are usually placed
on separate lines.
Eg: 1. SELECT ename, job... is a clause.
2. where job = 'CLERK' ; is a where clause.
• SQL STATEMENT:
– It is a combination of two or more clauses.
– Eg: SELECT *
From emp; is a SQL statement.