INNER JOIN
Returns only rows where there is a match in both tables. Rows without a matching key in either table are excluded.
Most common
Matching rows only
🗂️ Employees (Table A)
| id | name | dept_id |
|---|---|---|
| 1 | Alice | 10 |
| 2 | Bob | 20 |
| 3 | Carol | 10 |
| 4 | David | 30 |
| 5 | Eve | null |
🏢 Departments (Table B)
| id | dept_name |
|---|---|
| 10 | Engineering |
| 20 | Marketing |
| 40 | Sales |
🔍 Visual Match
Included from A
Included from B
Excluded
📋 Result
| emp_id | name | dept_id | dept_name |
|---|
📝 Generated SQL
💡 When to use INNER JOIN
Use when you only want rows that exist in both tables. Great for lookups where missing data should be silently dropped.
⚠️ Common mistake
Forgetting that NULL values never match in JOINs. If dept_id is NULL, that row disappears from an INNER JOIN result.
🚀 Performance tip
Ensure the joined columns are indexed. A missing index on dept_id turns a fast merge join into a slow nested loop.
📚 More resources
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