SQL Technique - Using Function Count() with condition Case in select statement

Source Code: 1- Create Table CREATE TABLE [dbo].[SaleInvoice]( [InvoiceNo] [varchar](50) NULL, [Dates] [datetime] NULL, [ItemCode] [varchar](50) NULL, [Qty] [int] NULL, [Price] [numeric](18, 2) NULL, [Amount] AS ([Qty]*[Price]), [Promotion] [varchar](50) NULL ) ON [PRIMARY] GO 2- Insert Data into Table by yourself 3- Write this script select ItemCode,Count(case when Promotion='Yes' then 1 end) as num_promotion from SaleInvoice group by ItemCode