Hello Sumukan,
you can solve this with a join between the input parameter table and the database table. E.g.
lt_res = select t2.consumer, sum(t2.sales) from :it_input as t1 inner join "<schema>"."<table>" as t2 on t1.consumer = t2.consumer and t1.datelow <= t2.date and t1.datehigh >= t2.date group by t2.consumer;
Consider that you have to replace the input parameter, schema/table name and column names with your values (cause I don't know it).
Best Regards,
Florian