- Essential one or more (inner) queries within an (outer) query
- Inner and outer query
- Not to be confused with inner and outer joins
- Inner query can go in three places
- SELECT clause (projection list)
- Must return a single value, then aliased as attribute in outer result
- FROM clause
- Inner query result used as standard table in FROM cross product
- WHERE clause
In Focus
2.1.21. Nested queries