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title: Limit the Use of unique()
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# Limit the Use of unique()

`unique()` can affect query performance for large datasets that have over 100 million rows and include more than one million unique values. For large datasets, `unique()` is faster for measures than for dimensions. If counting the number of unique string values causes performance issues, convert the string to a number. For example, use a hash of the string value or refer to the index of the string in a sorted list of string values.

**note:** Counting unique values can impact performance, but counting the total number of rows in a dataset doesn’t.