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Pandas Medium Theory

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merge vs join vs concat in pandas

`merge` combines rows by key columns, `join` is index-oriented sugar, and `concat` stacks objects along an axis.

• merge is SQL-like
• join defaults to index alignment
• concat appends rows or columns

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merge vs join vs concat in pandas

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SQL Easy Theory

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Explain SQL joins

Joins combine rows from tables based on a related key, with inner and outer joins deciding what unmatched rows survive.

• INNER keeps matches
• LEFT keeps all left rows
• Join condition matters

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Explain SQL joins

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SQL Easy Theory

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What are common SQL join types and when do you use them?

Inner joins return matches, outer joins preserve unmatched rows from one or both sides depending on the type.

• INNER for only matches
• LEFT when you need all left rows
• FULL when you need everything from both sides

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What are common SQL join types and when do you use them?

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