Guided Notes

Joins

Combining tables with INNER, LEFT, RIGHT, and FULL JOIN.

Why join?

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Real data is split across tables that share a key. A licenses table records each repository's license; a sample_files table lists each repository's files. Both have repo_name.

A JOIN combines them so one query can answer questions that need both β€” like "how many files are covered by each license?"

Splitting data this way avoids repeating the same information in thousands of rows.