Merging & Joining DataFrames

Summary

Pandas' equivalent of SQL joins — combining two DataFrames on a shared key using pd.merge(), with the same inner/left/right/outer logic from Phase 3.

• 1Practice a left merge between two related DataFrames (e.g. orders and customers).
• 2Compare the Pandas merge syntax directly to the SQL JOIN you'd write for the same result.
• 3Learn to check for unexpected row-count changes after a merge (a common bug source).