A heavy GROUP BY with a wide table is slow. Suggest two approaches to reduce work without changing results.

Problem Statement

Explanation

Project only needed columns before the GROUP BY using a subquery so fewer bytes flow through sort or hash. If the grouping key has an index that matches the order, use an index-ordered scan to avoid a full sort. Pre-aggregate upstream where possible, or use partial aggregation by partition key. In some engines, materializing to a temporary table and indexing the group keys first reduces spills and memory pressure.

Code Solution

SolutionRead Only

SELECT k, SUM(v)
FROM (
  SELECT key AS k, value AS v FROM big_table WHERE dt>=:d
) s
GROUP BY k;

Practice Sets

This question appears in the following practice sets:

Query Plans & Performance Tuning

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A heavy GROUP BY with a wide table is slow. Suggest two approaches to reduce work without changing results.

Problem Statement

Explanation

Code Solution

Practice Sets

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Which SQL statement retrieves all columns and rows from a table named employees?

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Master Interviews Anywhere, Anytime

A heavy GROUP BY with a wide table is slow. Suggest two approaches to reduce work without changing results.

Problem Statement

Explanation

Code Solution

Practice Sets

Related Questions

Which SQL statement retrieves all columns and rows from a table named employees?

Which clause filters rows before aggregation and affects which rows are grouped?

What is the default sort order when ORDER BY is used without ASC or DESC?

Which construct is commonly used to paginate results in SQL engines like Postgres and MySQL?

Which predicate correctly checks for missing values in standard SQL?

More from SQL & Databases

Master Interviews
Anywhere, Anytime