SQL · Intermediate
Correlated Subqueries
A correlated subquery references columns from the outer query. It is evaluated once for each row processed by the outer query to perform row-specific logic.
Open snippet →Code library
Intermediate SQL exercises
Read these Intermediate SQL snippets line by line — each one comes with a written breakdown of what the code does and why.
SQL · Intermediate
Common Table Expressions (CTEs)
A CTE is a temporary result set that you can reference within another statement. It improves readability by breaking down complex queries into logical blocks.
Open snippet →SQL · Intermediate
Filtering Aggregated Data with HAVING
The HAVING clause filters groups created by the GROUP BY clause. Unlike WHERE, which filters individual rows, HAVING filters based on aggregate function results.
Open snippet →