INTERSECT clause in Oracle, SQL Server and MySQL

INTERSECT clause is used in oracle and SQL Server to retrieve the data which are exists in both the tables.i.e we can say common records present in both the tables.


select column1, column2,....
from table 1 [where clause]
select column1, column2 ... 
from table2 [where clause]

For example  Table1 and table2 as below

MINUS clause in Oracle, SQL Server and MySQL

Minus clause in oracle used to query the records which are exists in table1 but not in table2.

select * from table1

select * from table 2


select column1, column2... from table1

select column1, column2... from table2

Make sure the data types for the columns should be compatible.

Normalization in Database

Normalization is the process of decomposing the relations (Tables) into smaller and well structured relations, to avoid the data redundancy. (or)

Normalization is the process of deciding which attributes should be grouped in a table to avoid the data redundancy in database.

There are some rules in the normalization each rule is called a normal form.

1. First Normal form (1NF)
2. Second Normal form (2NF)
3. Third Normal form (3NF)
4. Fourth Normal form (4NF)
5. Fifth Normal form (5NF).

Data Modelling in Dataware house

In Data warehouse dimension modelling is used. Dimension model is designed using fact and dimensions.

There are 3 types of schemas used in dimension modelling.

1. Star schema
2. Snowflake schema
3. Galaxy schema

1. Star schema:

In star schema center of the star is fact table and corners are dimension tables. In star schema dimension tables don't have parent tables. In star schema dimension tables are denormalized. It is efficient in query processing.

Star Schema
Star Schema

2. Snowflake schema:

In snowflake schema dimension tables have one or more parent tables. Snowflake schema efficient in transaction processing.

Snowflake Schema
Snoflake Schema

3. Galaxy schema:

Multiple facts tables connected with multiple dimension tables. Also referred as multi star schema.

Galaxy Schema
Galaxy Schema

Data Warehouse Concepts

Types of tables in Data warehouse:

1. Dimensions
2. Facts

Dimensions: These are attributes about facts.  Dimensions stores textural description about the business.

Facts:It stores business measurements. Facts are actual  transactions or values being analyzed.  They contain composite primary key where each attribute of primary key is a foreign key to the dimension table.

Fact table consists of keys and measures.

Performance Testing using JMETER

Performance testing is a process of checking if your applications can withstand the desired load. It is a process to ensure the code changes do not break or reduce performance of the existing application. In principle it is a meticulous process to ensure that applications response times are within the limits under the needed load conditions.

Peak Load:
It is the number of transactions or requests that the application is expected to get during the peak hour of Website/Application.