When any file is attempted to edit without any arguments (example ed or edit), the last SQL command is saved in AFIEDT.BUF, It acts like a default buffer file for edit commands.

1) START- Used to run a SQL script.
2) ACCEPT- Accepts input from user.
3) GET- Gets the sql file from user to place in buffer.
4) LIST- Displays the last command executed.
5) RUN- Used to list and run the command in buffer
6) SHOW- Shows the environment settings. Example: SHOW PAGESIZE

SQL*plus allows SQL and PL/SQL scripts to interactively run in command line.

It allows three kinds of commands to run; SQL, PL/SQL and SQL * Plus commands. It’s most commonly used by DBA’s to interact with the oracle database.

- ABS(number)

Returns the absolute positive value of an expression.
Syntax:
ABS(expression)
Example:
SELECT ABS(-1.0), ABS(0.0), ABS(1.0)
Output:
1.0    .0    1.0

- CEIL(number)

Returns the smallest integer greater than, or equal to, the specified numeric expression.
Syntax:
CEILING(expression)
Example:
SELECT CEILING($223.45), CEILING($-223.45), CEILING($0.0)
Output:
224.00    -223.00        0.00

- FLOOR(number)

Returns the largest integer less than, or equal to, the specified numeric expression.
Syntax:
FLOOR(expression)
Example:
SELECT FLOOR($223.45), CEILING($-223.45), CEILING($0.0)
Output:
223.00      -224.00        0.00

- MOD(number, divisor)

Returns the remainder of the division from 2 integer values.
Syntax:
MOD(dividend, divisor)
Example:
SELECT MOD(20,3)
Output:
2

- POWER(number, power)

Returns the exponential value for the numeric expression.
Syntax:
POWER(number, power)
Example:
SELECT POWER(2.0, 3.0)
Output:
8.0

- SIGN(number)

Returns the sign i.e. positive or negative value for the numeric expression. It returns -1 for negative expressions, a value of 0 for zero
Syntax:
SIGN(number)
Example:
SELECT SIGN(4)
Output:
1

- ROUND(number, precision)

Returns the numeric value rounded off to the next value specified.
Syntax:
ROUND(number, number of places)
Example:
SELECT ROUND(1.3456, 2)

- SQRT(number)

Returns the square root value of the expression.
Syntax:
SQRT(number)
Example:
SELECT SQRT(4.0)
Output:
2.0

- TRUNC(number, precision)

Returns a numeric value that truncate to the specific places
Syntax:
TRUNCATE(number,places)
Example:
SELECT TRUNCATE(1.3456, 2)
Output:
1.34

Aggregate functions in SQL are used to perform calculation on data. These functions are inbuilt in SQL and return a single value.

SUM( )

SUM function returns the sum or addition of all NOT NULL values of a column. For e.g. I have a Table employee with the fields id, name, salary and I want the sum of all salaries, I can use SUM function as shown
SELECT SUM(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 63,000

AVG( )

 
AVG function returns the average of all NOT NULL values of a column. For e.g. I have a Table employee with the fields id, name, salary and I want the average of all salaries, I can use AVG function as shown
SELECT AVG(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 21,000

COUNT( )

COUNT function returns the number of rows or values of a table. For e.g. I have a Table employee with the fields id, name, salary and I want the count of all rows, I can use COUNT function as shown
SELECT COUNT(*) from employee;

Max ( ) and Min ( )

MAX function returns the largest value of a column in a table. For e.g. I have a Table employee with the fields id, name, salary and I want the maximum salary of an employee, I can use MAX function as shown
SELECT MAX(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 22,000

MIN function returns the smallest value of a column in a table. For e.g. I have a Table employee with the fields id, name, salary and I want the minimun salary of an employee, I can use MIN function as shown
SELECT MIN(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 20,000

RDBMS is a database management system based on relational model defined by E.F.Codd. Data is stored in the form of rows and columns. The relations among tables are also stored in the form of the table.

Features:
- Provides data to be stored in tables
- Persists data in the form of rows and columns
- Provides facility primary key, to uniquely identify the rows
- Creates indexes for quicker data retrieval
- Provides a virtual table creation in which sensitive data can be stored and simplified query can be applied.(views)
- Sharing a common column in two or more tables(primary key and foreign key)
- Provides multi user accessibility that can be controlled by individual users

-  A stored procedure can accept parameters while a trigger cannot.
-  A trigger can’t return any value while stored procedures can.
-  A trigger is executed automatically on some event while a stored procedure needs to be explicitly called.
-  Triggers are used for insertions, update and deletions on tables while stored procedures are often using independently in the database.
-  A trigger cannot be written in a stored procedure. However, the reverse is not possible.

-  The process of having a copy of redo log files is called mirroring.
-  It is done by creating group of log files together. This ensures that LGWR automatically writes them to all the members of the current on-line redo log group.
-  In case a group fails, the database automatically switches over to the next group. It diminishes the performance.