Can JOINs cause duplicate rows in results? How do you eliminate them?

Use DISTINCT to return only unique combinations of selected columns.

Use GROUP BY to collapse rows (only when grouping makes sense).

Refine JOIN conditions to avoid unintended matches.

Normalize data to prevent duplicate stored values.

Use EXISTS instead of JOIN when only existence needs to be checked.

Understand the relationship (one-to-one, one-to-many, many-to-many).

Use DISTINCT only when logically correct—it hides problems instead of fixing them.

Use GROUP BY when aggregating data, not just to remove duplicates.

Avoid unnecessary JOINs when simpler EXISTS queries suffice.