How To Use dccount get estimate in Kusto Query Language | Kusto Query Language Tutorial KQL 2022

Topic: How To Use dccount get estimate in Kusto Query Language 

In this article, we are going to learn about dccount function, dccount function returns, and estimate for a number of distinct values that are taken by scalar expression in the summary group, Kusto Query Language is a powerful tool to explore your data and discover patterns, identify anomalies and outliers, create statistical modeling, and more. The query uses schema entities that are organized in a hierarchy similar to SQL's: databases, tables, and columns.

 // dcount - Returns an estimate for the number of distinct values that are taken by a scalar expression in the summary group.  
 //create Table and Insert Sample Data in Azure Data Explorer DB for Testing  
 .drop table TotalSale  
 .create table TotalSale (  
   id: int   
   ,SalePersonFName: string  
   ,SalePersonLName : string  
   ,ProductName : string  
   ,ItemsSold : int  
   ,SoldPrice :real  
   ,SoldDate: date  
   ,City : string  
   ,State : string  
   ,Country : string  
   ,Region : string  
      //Insert data  
       .ingest inline into table TotalSale <|  
 11,Tamara,Tony,Cell Phone,2,1200,2015-03-03,Frankfurt,Hesse,Germany,Europe  
 3,Christy,Ladson,TV,3,1600,2015-04-02,High Point,NC,USA,North America  
 7,Chirag,Patel,Cell Phone,5,1500,2015-06-23,AhmadAbad,Gujrat,India,Asia  
 2,M,Raza,Cell Phone,2,800,2015-07-15,Charlotte,NC,USA,North America  
 4,John,Rivers,Laptop,5,2400,2014-03-09,Jersey City,NJ,USA,North America  
 1,Aamir,Shahzad,TV,1,700,2015-07-15,Charlotte,NC,USA,North America  
 12,aamir,Shahzad,TV,1,7000,2015-07-15,Charlotte,NC,USA,North America  
 // get distinct rows  
 | distinct Country,City  
 // get distinct count by using distinct, Distinct is expencive when we have large amount of data  
 | distinct Country,City  
 | summarize CityCount=count(City) by Country  
 // we can use dcount to get estimated counts.   
 | summarize CityCount=dcount(City) by Country  
 //Accuracy     Error (%)     -- By default dcount uses 1 Accuracy  
 //0         1.6       
 //1         0.8       
 //2         0.4       
 //3         0.28       
 //4         0.2       
 // Second parameter let you set the accuracy  
 | summarize CityCount=dcount(City,0) by Country  
 | summarize CityCount=dcount(City,1) by Country  
 | summarize CityCount=dcount(City,2) by Country  
 | summarize CityCount=dcount(City,3) by Country  
 | summarize CityCount=dcount(City,4) by Country  

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