SQL: INNER JOIN keeps matches, LEFT JOIN keeps the left side too

The difference only shows on rows with no match. INNER drops them; LEFT keeps them and fills the right-hand columns with NULL.

Code

SELECT c.name, o.id
  FROM customer c
  JOIN orders o ON o.customer_id = c.id;      -- customers WITH orders

SELECT c.name, o.id
  FROM customer c
  LEFT JOIN orders o ON o.customer_id = c.id; -- every customer

Output

INNER: Ann | 1
       Ann | 2
LEFT:  Ann | 1
       Ann | 2
       Bob | NULL     <- Bob has never ordered

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Published 2026-08-25