when wil we use select 1 from empselect 2 from emp.....(In real time)

Please explain in detail

when we will use select 1 from table_Name?

select 2 from Table_Name?

select 3 from Table_Name?

what is the use of those statements.

when will we use those statement , where it useful in realtime.

i need explanation with clearly.

When you specify a number that means you are accessing column using its Index

here the output wil come how many rows are their on that table

that much rows comes with 1 or 2.

nothing but 1 or 2 will come how many record in their in table rows.

ex: let table  have 5 records

simple

1

1

1

1

1

(5 records)

like this its show. when will use in real time. that i need.

some time its used if exit(select 1 from emp where empid=101).

is it correct reason for that?

i need correct reason.

thanks for greate response.

Actually the Index feature is meant for Order By clause. Example

SELECT CustomerId, ContactName FROM Customers
ORDER BY 2 ASC

The above will Order the results by ContactName as it is Index is 2

while the below one will Order the results by CustomerId

SELECT CustomerId, ContactName FROM Customers
ORDER BY 1 ASC