Practice vocabulary for describing SQL JOIN types including INNER, LEFT, CROSS, self-joins, and many-to-many relationships.
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Which JOIN type returns only the rows where there is a matching value in both tables?
INNER JOIN returns only matching rows — rows that have a corresponding record in both the left and right tables.
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You need to retrieve all customers even if they have never placed an order. Which JOIN should you use?
LEFT JOIN preserves all left-table rows, filling right-side columns with NULL when no matching row exists in the right table.
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A CROSS JOIN between a table of 10 rows and a table of 5 rows produces how many rows?
A CROSS JOIN is a Cartesian product — every row from the left table is combined with every row from the right table: 10 × 5 = 50 rows.
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To find an employee's manager when both employees and managers live in the same 'employees' table, you would use a _____.
A self-join joins a table to itself, commonly used to traverse hierarchical relationships stored in a single table (e.g., employee → manager).
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When a many-to-many JOIN produces far more rows than expected because of duplicate join keys, developers call this a _____.
A many-to-many explosion occurs when both sides of a JOIN have multiple matching rows per key, multiplying the result set to an unexpectedly large size.