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While correlated subqueries are useful, they have a significant drawback: performance. Avoid them whenever possible, especially in performance-sensitive contexts or when the same result can be achieved using joins or non-correlated subqueries, and always verify performance by examining the execution plan. So, basically:
- Don’t use when performance is critical, especially with large datasets due to possibly time complexity
- Try to replace correlated subqueries with joins, which tend to execute faster because they can process data in a more set-based manner rather than row-by-row
- Check the execution plan to see how the database intends to run the query. Sometimes, correlated subquery may not be problematic since db optimizes the query