How to aggregate values in rows based on condition and getting output in sql?

My table contains few rows, which has to be aggregated. eg: Columns are sites, fuel, sales, date when date ,sites and fuel is same I need to aggregate the sales column for those rows and have one row.( delete other rows or not to select those rows, since values are aggregated)

How can I do that simply in select query in sql?

eg

site, fuel, sale,date
siteA, Diesel, 100, 2019-01-01
SiteA, Diesel,  300, 2019-01-01
siteB ,Ulp, 200, 2019-01-01
siteC,E10, 500, 2019-01-01

Output has to be;

site, fuel, sale,date
siteA, Diesel, 400, 2019-01-01
siteB ,Ulp, 200, 2019-01-01
siteC,E10, 500, 2019-01-01

My sql is like;

 select 
        [CompanyCode] as 'Company Code',
        [Sitecode] as 'Site Code',
        [ProductCode] as 'Product Name',
        CONVERT(date, [InvDay]) as  Date,

         SUM (CASE
                    WHEN [Sales] ='NULL' THEN 0
                     WHEN [Sales] = '' then 0
                    ELSE
                     CONVERT(decimal(10,4) ,[Sales] )
                     END) as 'Sale Volume'

    FROM [dbo].[2018-01] 

     group by Companycode,Sitecode,ProductCode,date,Sales

Answer

Use group by and sum() aggregation

select  site, fuel, date, sum(case when sales is null or sales='' then 0 else cast(sales as decimal(10,4)) end) as sale
from tablename
group by site, fuel, date

As per your answer – you’ve to remove sales column from group by

select 
        [CompanyCode] as 'Company Code',
        [Sitecode] as 'Site Code',
        [ProductCode] as 'Product Name',
        CONVERT(date, [InvDay]) as  Date,

         SUM (CASE
                    WHEN [Sales] is null or
                     [Sales] = '' then 0
                    ELSE
                     CONVERT(decimal(10,4) ,[Sales] )
                     END) as 'Sale Volume'

    FROM [NEO_DB].[dbo].[Caltex-migration-2018-01] 

     group by Companycode,Sitecode,ProductCode,CONVERT(date, [InvDay])