Which one of the following actions will definitely not reduce any query cost?

Question

BlackTom AI · Accepted Answer

The question asks us to evaluate actions in terms of their impact on query cost. 
Option 1: 'Rewrite query to select all columns of a table instead of some particular columns' – this is typically detrimental to performance because it forces the database to read and return more data than necessary, increasing I/O, memory usage, and network transfer without providing additional value. Therefore, it will not reduce cost and often increases it.
Option 2: 'Rewrite query with parameters' – parameterized queries can help the database engine reuse execution plans and improve caching, which often reduces parsing and planning overhead and can lead to faster execution for repeated queries. This is generally a cost-reducing or cost-stabilizing practice.
Option 3: 'Create an index' – adding an index can dramatically reduce query cost by enabling faster data retrieval, especially for selective predicates, leading to lower I/O and quicker lookups.
Option 4: 'Store derived data' – materializing derived data (e.g., using a materialized view or cached results) can avoid expensive recomputation and reduce runtime cost for repeated queries.
In summary of the reasoning for each choice: increasing data retrieval by selecting all columns tends to increase cost, while parameterization, indexing, and derived data storage are common techniques that typically lower or stabilize query cost by improving plan reuse, access paths, or precomputing results. The analysis shows that the first option is the one that does not reduce cost and is, in most cases, detrimental to performance.

COMP90050_2025_SM2 Quiz 2

Which one of the following actions will definitely not reduce any query cost?

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