Join Types

Control which rows are kept when merging with the how parameter.

Inner Join (Default)

Keep only rows that match in both DataFrames:

Left Join

Keep all rows from left, match from right:

Right Join

Keep all rows from right, match from left:

Outer Join

Keep all rows from both DataFrames:

Comparison of All Join Types

Cross Join

Every row paired with every other row:

Exercise: Left Join

Exercise: Outer Join

Key Points

• how='inner' - only matching rows (default)
• how='left' - all from left, matching from right
• how='right' - all from right, matching from left
• how='outer' - all rows from both
• how='cross' - all combinations (cartesian product)
• Unmatched values become NaN