Selectivity and Estimated Row: Variable
SQL Server does not sniff for variable, it just simply uses the fixed value. I'm going to use AdventureWorks 2019 in this post. --------------------Please run this script--------------- use AdventureWorks2019 go IF exists(select 1 from sys.tables where name='SalesOrderDetail' and schema_id=schema_id('dbo')) drop table SalesOrderDetail go select * into SalesOrderDetail from [Sales].[SalesOrderDetail] go create statistics iProductID ON SalesOrderDetail(productid) with fullscan go dbcc traceon(3604,2363)---trace flag 2363 displays more detail about the selectivity go --------------------Please run this script--------------- Equality(=): all density DECLARE @pid INT = 0 SELECT * FROM SalesOrderDetail WHERE ProductID = @pid 456= 'All density'*card =0.003759399*121317(note, if there new rows inserted or deleted, you have to replace the 121317 with current card) DBCC execution completed. If DBCC printed error messages, contact your system administ