What is "Using covering Indexes"

Using covering Indexes
As mentioned earlier, when you insert an or update a record, any data in a column, which is included in
An index was stored not only in the table, but also in the indexes for nonclustered indexes. From finding
An entry in a index, SSE then moves to the table to locate and retrieve the record. However, if
The necessary information is held within the index, there are no need to go to the table and retrieve
The record, providing much speedier data access.
For example, consider the Sharedetails.shares table in the Apressfinancial database. Suppose
That's the description, current price, and ticker ID of a share for wanted to find. If an index
was placed on the Shareid column, knowing a identifier column and therefore unique,
You would ask SSE to find a record using the ID supplied. It would then take the details from the
The index of where the data is located and moves to that data area. If, however, there was a index with
All of the columns defined, SSE would be able to retrieve the description ticker and price details in the
Index action. It is not being necessary to move to the data area. This is called a covered index, since
The index covers every column in the table for data retrieval.