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## count_distinct

count_distinct — aggregate function to return the count of rows in the specified column that have distinct values

## SYNOPSIS

`count_distinct (`expr`)`

## DESCRIPTION

This function returns the count of rows in the specified column that have distinct values. The `expr` argument must be a literal column name in the current table, or a simple expression that resolves to a column name.

## EXAMPLE

This example shows how to use dynamic aggregation using this function. In the Hello LiveView sample, create a query that finds the count_distinct value from a column of the ItemSales table. Follow these steps:

1. In LiveView Desktop connected to a server running the Hello LiveView sample, select the ItemsSales table from the Tables pane of the LiveView Tables view.

2. In the Select field, enter:

       count_distinct(Item) as NumItems

3. Make sure the Query field is empty.

4. Click Open Query.

The query results open in a grid view. LiveView Server recalculates the NumItems value whenever the rows returned by the query predicate change.

## SEE ALSO

This LiveView aggregate function is based on the count_distinct aggregate function in the StreamBase expression language.