please in the future limit your questions in a single post
Q2 your thought process is stuck in working with spreadsheets that are "Cell based" - tableau is data base driven using dimensions and measures -
If you want to search "across rows" and teh values in that row come different dimensions then you will need to search each dimension independently
Q3 Parameters are the way users input a single value into tableau - they are static and are global (affect the entire workbook) and must be backed up with a calculated field to be used in a viz
Q4 - the answer goes back to Q2) but yes you can use countd () in an it then statement
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