Because array index shows distance from the 1st element. Since the first element is zero distance away from itself, index starts from zero. The next element will be "index*scaling factor" distance away from 1st element. In case of integer array next elements will be  1*2, 2*2, 3*2, 4*2, .................bytes  away from the first element .

Clustered index  physically arranges all data in a table in a sequential manner. We can not have more than one physical arrangements of data in a table, so we can have only one clustered index per table.

Fill factor is a defiened percentage between 0 to 100 in which we leave exra gaps to accomodate future
expansions in the storage of the futures data.
Indexing in sql is same as the index in our books. it helps us to manage our data more appropriately.it can be
done in two ways namely clustered index and non-clusterd index.we can create only one clustered index per table and maximum of 249 non-clustered indexes per table.

--> Stored Procedures Advantages    Stored Procedures are precompiled one.    it is the group of sql statements.     stored procedure like a application programming.     stored procedure is a fast one because it is already precompiled.     stored procedure is the one is easy to maintain. --> Triggers Advantages     Triggers is a special kind of procedure.    the Main advantage of the trigger is automatic.     whenever the table affected by insert update or delete     query that time the triggers will implicitely call. --> Indexes Advantages     The Main advantage of the indexes is speed.     if the table having the indexes while selecting or filtering the row(s) 0r
columns(s) ,the execution time very fast.but,if you use the indexed table
the insert update and delete will be slow.

We can improve the speed by creating the index on necessary fields.