INNER JOIN vs LEFT JOIN
INNER JOIN keeps matches only; LEFT JOIN preserves every row from the left side.
INNER JOIN
Use it when
Use LEFT JOIN to detect missing matches.
LEFT JOIN
Use it when
Use INNER JOIN when unmatched left rows should not appear.
Decision rule
Choose the option that matches the real requirement, data size, maintainability needs and compatibility constraints. Avoid selecting a technique only because it is familiar.
Need clarity?Prefer the simpler option that expresses the business rule directly.
Verify before scaling
Run both approaches on a small known dataset if the difference affects financial, inventory or operational decisions. Equivalent-looking techniques can behave differently with duplicates, blanks, NULL values or version constraints.