Is there any property in the a!queryEntity to select distinct values from a DB table.
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What's your use case? There are fairly easy ways to de-duplicate data post querying, or to aggregate data during a query, but importantly, Appian queries don't really work like SQL statements.
a!queryAggregation( aggregationColumns: { a!queryAggregationColumn( field: "distinctColumn", isGrouping: true ),
Just to follow up on Mike's comment...there are a number of set-processing functions that you can use in Appian to post-process the retrieved data. fn!union() is the one that would de-duplicate your data.