Oracle Questions

The number of rows returned by a select query can be restricted by the LIMIT clause.
Example:
SELECT * from employee
LIMIT 20

-  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.

Even though both PL/SQL and Java (or) .NET can be used, PL/SQL stands above these two in terms of integration overhead. This is because Java is an open source proprietary and Data manipulation is slightly faster in PL/SQL than in Java. 

Joins are used to combine data of one or more tables. Joins should be used when there is abundant data. Joins can be LEFT, RIGHT, OUTER, INNER or even SELF JOIN. The purpose is to bind data from multiple tables without any receptivity

The CACHE option means how many sequences will be stored in memory for access by the application objects. The performance is faster. However in case of the database is down the data is memory is lost for the sequence.

The NO CACHE option means values are not stored in memory. So there might be some performance issue. 

Oracle database comprises of three kinds of files:
- Datafiles
- Redo log files
- Control files

Oracle NOT NULL is used on a column to ensure that the value for that column can never be NULL.
Example:
Below, the constraint is that the id should never be NULL. If it is, oracle throws an error.
create table employee ( id number NOT NULL, Name varchar(200) );

- 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