How can a Non-Clustered index output a column that is not included in the index

Question

Viewing the Execution plan, i see \"column A\" in the Output List. The operation is an Index Scan on a Non-Clustered Index : \"IX_name\"

When i see the definition of

Answer 1

Internally, a non-clustered index contains all key columns of the clustered key. This is to support the key lookup operation and to ensure that internally each index row has a unique key. For heaps each NCI contains the row bookmark for the same reasons.