10 customers, 4 with orders. How many rows does a LEFT JOIN give?

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Accepted Answer

Ten, with NULL order columns for the six that have none — A LEFT JOIN keeps all ten left-hand rows and fills the right-hand columns with NULL where nothing matched. Four is the inner join, six is what you get by adding WHERE orders.id IS NULL, and fourteen would need a FULL OUTER JOIN with unmatched rows on both sides.

Answer

Four, since only the customers with orders can match

Answer

Six, returning just the customers who never ordered

Answer

Fourteen, the matches plus every unmatched row of both

10 customers, 4 with orders. How many rows does a LEFT JOIN give?

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