A Common Table Expression (CTE) in SQL is a named temporary result set, derived from a SELECT statement, that can be used within another SELECT, INSERT, UPDATE, or DELETE statement. It is defined using the WITH clause followed by a SELECT statement and a name for the CTE, and can be referred to by name in the main query. CTEs are useful for breaking down complex queries into simpler, more readable parts, and can also improve query performance by reducing the need to repeat subqueries.
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