Question

On SQL explain Views, Union All,  Union, Truncate, Delete. And how we create Accounts in SQL Server?

Answer 1

Views:
Views provides encapsulation like it hides the original name of table. In view one can use more than one tables from database and add some sql functions, joins, where condition to get desire output. Basically it has rows and columns just like real table.

Example:
CREATE VIEW view_name AS
SELECT [column1], [column2] FROM table_name WHERE condition

You can also update and drop views.

Union All:
This combines result set of two or more select statments with duplication of rows. To use Union All you need to select same number of columns with same datatype and columns are specified in same order.

Example:
SELECT [Name],[Gender] FROM CITY1_TABLE WHERE [AGE] >18
UNION ALL  
SELECT [Name],[Gender] FROM CITY2_TABLE WHERE [AGE] >18

Union:
This combines result set of two or more select statements with distinct row. It never returns duplicate rows. To use Union you need to select same number of columns with same datatype and columns are specified in same order.

Example:
SELECT [Name][Age] FROM CITY1_TABLE where condition
UNION  
SELECT [Name],[Age] FROM CITY2_TABLE where condition

Truncate:
Truncate command will delete data present in table but it does not delete the table itself.

Example:
TRUNCATE TABLE table_name

Delete:
Delete command will delete existind records in table.

Example:
DELETE FROM table_name  WHERE condition

Create Account in SQL Server:

To create Login:
Navigate to Security -> Logins -> New Login and enter Login name, Password, Confirm Password and click OK to save.
or using query:
CREATE LOGIN login_name WITH PASSWORD = 'password';