Bitmap index concept: is it defined as an index on columns from two or more tables sharing the same value domain, or is that description incorrect?
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AValid — that is the definition of a bitmap index
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BInvalid — bitmap indexes map distinct values to bitmaps in a single table
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CValid only when the index is composite
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DValid for foreign keys but not primary keys
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EValid exclusively in columnar databases
Answer
Correct Answer: Invalid — bitmap indexes map distinct values to bitmaps in a single table
Explanation
Introduction / Context:This question checks whether you can distinguish a standard bitmap index from related concepts such as a bitmap join index. Bitmap indexes are common in analytic workloads for low-cardinality columns.
Given Data / Assumptions:
- A bitmap index stores a bitmap for each distinct value of a column, indicating row positions where the value occurs.
- They are typically built on one table's column, enabling fast boolean combinations.
- A bitmap join index exists in some products and precomputes a join condition, but that is different from the basic definition.
Concept / Approach:The prompt’s wording (“columns from two or more tables”) corresponds more to a join index, not to the general definition of a bitmap index. Therefore the statement is invalid.
Step-by-Step Solution:Recall: bitmap index = value-to-bitmap mapping for a column in a table.Note: boolean operations on bitmaps accelerate multi-predicate filters.Contrast: bitmap join index pre-joins tables — a specialized feature.Conclude the given description does not match a standard bitmap index.
Verification / Alternative check:Vendor docs show separate entries for “bitmap index” and “bitmap join index,” reinforcing the distinction.
Why Other Options Are Wrong:Composite keys, foreign-key focus, or columnar storage do not redefine the basic bitmap index concept.
Common Pitfalls:Equating all bitmap-based optimizations with the term “bitmap index.”
Final Answer:Invalid — bitmap indexes map distinct values to bitmaps in a single table