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The COUNT_DISTINCT function counts the number of unique items in a field.
Syntax
COUNT_DISTINCT( X )
Parameters
X - a field or expression that contains the items to be counted.
How the COUNT_DISTINCT function works
The COUNT_DISTINCT function takes 1 parameter, which can be the name of a metric, dimension, or expression of any type. COUNT_DISTINCT returns the total number of unique items in that field or expression.
To count all items, including duplicates, use COUNT.
In a data source, change a field's Aggregation type to Count Distinct.
You can't apply this function to a pre-aggregated field ( Aggregation type of Auto ), or to an expression which is the result of another aggregation function. For example, a formula such as COUNT_DISTINCT(Sessions) in a Google Analytics data source will produce an error.
To avoid possibly incurring higher query costs when using BigQuery data sources, consider using APPROX_COUNT_DISTINCT.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-07-22 UTC."],[],[],null,["# COUNT_DISTINCT\n\nThe `COUNT_DISTINCT` function counts the number of unique items in a field.\n\nSyntax\n------\n\n`COUNT_DISTINCT( `\u003cvar translate=\"no\"\u003eX\u003c/var\u003e` )`\n\n### Parameters\n\n- \u003cvar translate=\"no\"\u003eX\u003c/var\u003e - a field or expression that contains the items to be counted.\n\nHow the `COUNT_DISTINCT` function works\n---------------------------------------\n\nThe `COUNT_DISTINCT` function takes 1 parameter, which can be the name of a metric, dimension, or expression of any type. `COUNT_DISTINCT` returns the total number of unique items in that field or expression.\n\nTo count all items, including duplicates, use `COUNT`.\n| **Tip:** There are 2 other ways to apply this function:\n|\n| \u003cbr /\u003e\n|\n| - In a data source, change a field's **Aggregation** type to `Count Distinct`.\n| - in a report, [edit the field's aggregation](/looker/docs/studio/edit-fields-in-your-reports) in a chart.\n\nExamples\n--------\n\nLimits of `COUNT_DISTINCT`\n--------------------------\n\nYou can't apply this function to a pre-aggregated field ( **Aggregation** type of **Auto** ), or to an expression which is the result of another aggregation function. For example, a formula such as `COUNT_DISTINCT(Sessions)` in a Google Analytics data source will produce an error.\n\nTo avoid possibly incurring higher query costs when using BigQuery data sources, consider using `APPROX_COUNT_DISTINCT`.\n\nRelated resources\n-----------------\n\n- [Calculated fields](/looker/docs/studio/about-calculated-fields)\n- [Looker Studio function list](/looker/docs/studio/function-list)"]]
