What is a correlated subquery?

< 1 min read

A correlated subquery is a subquery that depends on values from the outer query.
It runs once for each row processed by the main query.
This is useful when comparisons are needed at a row level.
In my project, we used it to find orders higher than the customer’s average order value.
The subquery referenced customer_id from the outer query.
It makes logic clear but can impact performance on large datasets.
We used it carefully and tested execution time before production.

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