Explain the difference between RANK(), DENSE_RANK(), and ROW_NUMBER() window functions.
RANK(), DENSE_RANK(), and ROW_NUMBER() in MySQL 8.0
In MySQL 8.0, RANK(), DENSE_RANK(), and ROW_NUMBER() are window functions used to assign sequential numbers to rows based on a specified order. They differ in how they handle ties (rows with the same values in the ORDER BY clause).
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Assigns a unique sequential number to each row in the result set.
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Does not consider ties; every row gets a distinct number.
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Sequence always increments by 1.
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Assigns the same rank to rows with identical values in the ORDER BY clause (ties).
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Leaves gaps in the ranking sequence after ties.
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Useful when you want to reflect tie positions explicitly.
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Assigns the same rank to tied rows, similar to RANK().
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Does not leave gaps in the ranking sequence.
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Useful when you want consecutive ranking numbers even with ties.
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ROW_NUMBER() always gives unique numbers; ignores ties.
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RANK() gives tied rows the same rank and skips subsequent numbers.
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DENSE_RANK() gives tied rows the same rank but does not skip numbers.
In summary: Use ROW_NUMBER() for unique row numbering, RANK() when you need tie-aware ranking with gaps, and DENSE_RANK() when you need tie-aware ranking without gaps in the sequence.