beginner~4h
JOINs — INNER, LEFT, RIGHT, FULL, SELF, CROSS
JOINs combine rows from two or more tables based on a related column. Understanding which JOIN to use and how it executes is fundamental to SQL mastery.
Learning objectives
- Predict exactly which rows a query returns for INNER, LEFT, RIGHT, and FULL joins on two given tables.
- Explain, precisely, why putting a filter in ON versus WHERE can change a LEFT JOIN's results.
- Recognize when a SELF JOIN is the right tool, and write one correctly.
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JOINs — INNER, LEFT, RIGHT, FULL, SELF, CROSS