A database query performance issue arises when statistics are out of date. Which column statistics should you update to improve performance for a table?

A database query performance issue arises when statistics are out of date. Which column statistics should you update to improve performance for a table?

• A. Columns used in GROUP BY clauses
• B. Columns used in WHERE clauses
• C. Columns used in ORDER BY clauses
• D. All columns in the table

Answer: (A)

Statistics inform the optimizer about how data is distributed in each column, which influences cardinality estimates and plan choices. When statistics are outdated, the optimizer can misestimate how many distinct groups will be produced and how many rows fall into each group. For queries that use a GROUP BY, these estimates directly affect which aggregation method (and related operations like sorting or hashing) the plan will pick, as well as memory and CPU costs. Updating the statistics for the columns involved in the GROUP BY provides current distribution information, leading to more accurate plans and better performance. While refreshing stats on other columns can help too, the most impactful improvement for aggregation-heavy queries comes from keeping the GROUP BY columns up to date.

Statistics inform the optimizer about how data is distributed in each column, which influences cardinality estimates and plan choices. When statistics are outdated, the optimizer can misestimate how many distinct groups will be produced and how many rows fall into each group. For queries that use a GROUP BY, these estimates directly affect which aggregation method (and related operations like sorting or hashing) the plan will pick, as well as memory and CPU costs. Updating the statistics for the columns involved in the GROUP BY provides current distribution information, leading to more accurate plans and better performance. While refreshing stats on other columns can help too, the most impactful improvement for aggregation-heavy queries comes from keeping the GROUP BY columns up to date.