Does INCLUDing Columns to Non-Clustered Index DUPLICATE values?

Question

If I use INCLUDE clause and add some columns to a Non-Clustered Index, does this mean I am storing the data both on INDEX and on its PAGE -meaning at least DOUBLING the space consumed-?

Answer 1

Yes. This space doubling also goes for index keys. Indexes can make up a significant amount of storage space.

A covering index with all table columns will be almost exactly the size of the original table, just sorted differently.