Whісh соmmаnd wоuld уоu usе іn Lіnuх to shоw thе сurrеnt usеrs оn thе sуstеm?

What

is the purpose of adding indexes to the database?

The

table has column Ex_Col. There are 4 

records  which have  the next values in

Ex_Col

column {100, 200,300,NULL}. What will be the result of AVG(Ex_Col)?

Given these contents

of the Customers table:

How many  rows

will have the result of the next query

SELECT Name FROM Customers WHERE ReferredBy<>2?