USING clause

Overview

The USING clause is shorthand for specifying join conditions when two tables share one or more identically named columns. Instead of writing out a full ON equality condition, USING (col) joins on that column directly:

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SELECT *
FROM orders
JOIN customers USING (customer_id);

-- equivalent to:
SELECT *
FROM orders o
JOIN customers c ON o.customer_id = c.customer_id;

USING vs ON: the key difference in output

The two forms aren't purely stylistic -- they behave differently in the result set. USING (customer_id) produces a single, unqualified customer_id column in the output. ON o.customer_id = c.customer_id keeps both orders.customer_id and customers.customer_id as separate columns, which then need explicit qualification (or exclusion) if selected with SELECT *, since both tables have a same-named column.

Multiple columns

USING can list multiple shared columns to join on all of them simultaneously:

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SELECT *
FROM sales
JOIN inventory USING (store_id, product_id);

USING vs NATURAL JOIN

USING requires you to explicitly name the join columns, while NATURAL JOIN infers them automatically from every column name the two tables happen to share. USING is the safer, more maintainable middle ground: it avoids repeating a fully-qualified equality condition like plain ON requires, but it doesn't silently change behavior if an unrelated same-named column is added to either table later, since the join columns are pinned explicitly in the query text.

DuckDB notes

DuckDB supports USING across all join types (INNER, LEFT, RIGHT, FULL, and even ASOF JOIN, where USING treats the last listed column as the inequality condition rather than an equality). This makes USING a genuinely useful, DuckDB-idiomatic pattern beyond just a stylistic shortcut for ordinary equi-joins.