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Interview Questions and answers for beginners - SQL Server Day 11

Question: What is SQL?
Answer: SQL stands for Structured Query Language, which is use to retrieve, store and manipulate data in database.

Question: What is data?
Answer: In simple terms, the data can be considered an object of the relevant facts. For example your name, age, height, weight, image etc.

Question: What is Database?
Answer: physically collection of data in systematic way is called database. Database gives permission to manage data like store, retrieve and manipulate.
In one line Database is the collection data, schemas, tables, queries, reports, views, and other objects.

Question: What is table?
Answer: Table is the collection of data which have columns and rows. A table has a specified number of columns, but can have any number of rows.
Example: Student table

Name
Address
FatherName
DOB
Class
Dilip
Noida
PB Singh
09-12-2001
10
Anil
GKP
MG Singh
08-10-2002
9
Ashish
Delhi
DK Singh
12-02-2012
UKG

Question: What is field in column?
Answer: A column is the set of values. This is contains a particular data type value in table. It shows vertically in table. For Example above table contains columns Name, Address, FatherName, DOB and Class. Name is the column which contains student’s name.

Name
Dilip
Anil
Ashish

Question: What is RDBMS? 
Answer:
A Relational Database management system (RDBMS) is the Database management system in which we maintain data records in tables and relationship among and across the data and table. Relationship among the data is also stored in the form of table.

A Relational Database management system (RDBMS) is an additional condition which system supports a tabular structure of the data, with applies of relationships between tables.


A Relational Database management system (RDBMS) has the capability to recombine the data items from different files, providing powerful tools for data usages.

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What is difference between UNION and UNION ALL in SQL Server

We use UNION and UNION ALL operator to combine multiple results set into one result set.
UNION operator is used to combining multiple results set into one result set but removes any duplicate rows. Basically, UNION is used to performing a DISTINCT operation across all columns in the result set. UNION operator has the extra overhead of removing duplicate rows and sorting result.
UNION ALL operator use to combine multiple results set into one result set but it does not remove any duplicate result. Actually, this does not remove duplicate rows so it is faster than the UNION operator. If you want to combine multiple results and without duplicate records then use UNION otherwise UNION ALL is better.
Following some rules for using UNION/UNION ALL operator
1.The number of the column should be the same in the query's when you want to combine them. 2.The column should be of the same data type. 3.ORDER BY clause can be applied to the overall result set not within each result set.
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