Error in converting varchar to float in mssql server 2012 : I have imported large excel sheet in my sql db and all columns are by default varchar datatype.
I want to select sale volume in float(double) which is in varchar format.

My query is like this but i still get converting error. How can I overcome this conversion error?
 

    select 
    		[CompanyCode] as 'Company Code',
    		[Sitecode] as 'Site Code',
    		[Product] as 'Product Name',
    		'' as 'Tank ID',
    		CONVERT(date, [InvDay]) as  Date,
    		CAST([Sales] as decimal) as 'Sale Volume',
    		'' as 'Record ID'
    From [dbo].[2019-01]