Aggregations & Grouping

Guides to translating SQL GROUP BY, HAVING, and aggregate functions into ActiveRecord, including edge cases that break counts and summaries.

ActiveRecord group and count — SQL GROUP BY in Rails

How to use group and count in ActiveRecord for SQL GROUP BY. With having, order, and the SQL Rails generates. Rails 7/8 production examples with output.

September 23, 2026 3 min read

ActiveRecord select method performance comparing SELECT * vs specific columns showing 88% data transfer reduction

Added select() to Limit Columns. Performance Improved 40%. Stopped Loading Data I Didn't Need.

Added select() to stop loading unused columns. Response times dropped 40%. Here's the pattern, what to watch for with missing attributes, and when worth it.

April 02, 2026 8 min read

Rails find_each vs each batch processing comparison showing memory usage with 100K records

Rails find_each vs each—Why Background Jobs Need Batch Processing

Using each on large ActiveRecord collections loads all records into memory. find_each batches them. Here's why background jobs need this and the gotchas.

March 19, 2026 8 min read

LEFT JOIN + WHERE in ActiveRecord: The Trap That Turns It Into INNER JOIN

Adding WHERE after LEFT JOIN in Rails silently converts it to INNER JOIN. Here's why it happens, how to spot it, and the fix with .merge() or subqueries.

January 05, 2026 5 min read