Nested query
A nested query is a query embedded within another query or statement whose result participates in evaluating the containing operation.
Learn SQL in a Month of Lunches
A subquery is an SQL query nested within another SQL statement whose result can supply data for joining, filtering, or other operations.
- How it is used
- Combines multiple SELECT results into one statement for filtering, comparisons, and joins.
- How deep it goes
- Demonstrates WHERE, FROM, and SELECT placements plus multirow operators, while warning that SELECT-clause subqueries are rarely best.
- Examples
- Uses customer orders, titles in order 1034, Joe Pagenaud, Cora Daly, and the longest title name.
- What you can do after
- Apply it via SQL operators to filter, exclude, compare, and join results returned by nested SELECT statements.
Read how Learn SQL in a Month of Lunches explains nested query →
DuckDB in Action
A subquery is a query nested inside another SQL statement or expression.
- How it is used
- Stages analytical computations, filters rows against inner results, and prepares values for comparisons.
- How deep it goes
- Explains uncorrelated, scalar, correlated, and set-comparison forms with runnable examples, while deferring broader query optimization.
- Examples
- Demonstrates per-system power aggregation, maximum-reading filters, correlated maxima, joins, EXISTS, IN, ANY, and ALL.
- What you can do after
- Apply it in DuckDB to stage aggregates, filter by scalar results, correlate inner queries, and test membership or inequality across result sets.
Related concepts
- joinalternative to · A join is an operation that combines records or rows from multiple data sources according to specified matching conditions or relationships.
- NOT INused by · NOT IN is a SQL predicate that tests whether a value is absent from a specified list or subquery result, subject to null semantics.
- temporary tablealternative to · A temporary table is a database table created for transient use during a session or operation and removed automatically or explicitly when its relevant scope ends.
- membership operatoruses · A membership operator is a language construct that tests whether a specified value or property is present in a supported collection, range, or object.
- from clausepart of · A FROM clause is the SQL query component that specifies the tables or other data sources providing input rows.
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