Getting a table's column value to use in a custom filter

Very easy, follow the steps

1. Load the dataset using IMPORT from the table.

2. Left sidebar in your dataset window right click on the query and choose refrence.

3. Goto the refrence query and remove all other columns leave the column where you want distinct values. 

4. Right click the column and select remove duplicates. Close and apply.

Drag the column name from the refrence query on the slicer component and use first query fields on any other visual component. it will work.