Subqueries and CTEs: Asking a Question Inside a Question
Some questions can't be answered in one pass. "Which hive produced the most honey?" needs the maximum honey figure before it can find the hive that matches it. "Which keepers are above average?" needs the average before it can compare anyone to it. SQL handles this the same way you'd handle it on paper: work out the smaller number first, then use it. That's what a subquery is. A CTE does the same…
Subqueries and CTEs allow querying data within another query, like exploring a question inside another question. In the beekeeping co-op example, subqueries help find the hive with the most honey, hives that haven't been harvested, and each hive's most recent harvest. They work by performing smaller calculations first, then using the results in the main query.
A CTE (Common Table Expression) is similar but defined differently. It's a named temporary result set used within one query. The main difference is where you place it: inside a subquery or directly before the main query. Using a CTE can make complex queries easier to read and maintain by breaking them down into simpler, named steps.
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