Calculate (n) workdays from a given date, using a calendar table

As shown on below image, I have two tables; - **Customer** : with about 4 million records; and 3 columns [Customer] : Customer ID [Date] : Creation date [Num_Days] : Number of working days to calculate the [next_wkday] in the query result. - **Calendar** : with all calendar days; and 3 columns [ref_date] : dates [civil_util] : when (1) -> workday; when (0) -> non working day [year] I need to get the **query_result** with the three columns of Customer Table and a calculated date [next_wkday], representing the number of working days [Num_Days] after each customer Creation date, jumping the zeros (*non working days*) in the [civil_util] column. I've created the query below to calculate the [next_wkday] using the Lead() function. But is not a solution because the **offset parameter** must be a constant, and we need to use the [Num_Days] value for each Creation Date: select *, Lead (to_date(ref_date),5) OVER (ORDER BY to_date(ref_date)) AS next_wkday, datediff(Lead (to_date(ref_date),5) OVER (ORDER BY to_date(ref_date)),ref_date) as days_diff from calendar where ref_date >= to_date(now()) and civil_util = 1 limit 1 Basicaly I need to solve two problems: 1 - Must be a query to perform the calculation Because I don't have the profile to create functions in the database. 2 - I need to design a query that achive the ***Query result***, shown in the image, that will able to join both, the Customer table and the calculation query. So, I need to find another solution. And that solution must work in two engines: 1. Impala version : impalad version 2.12.0-cdh5.16.2 2. Oracle 11g I need to reinforce, for performance puposes, that the Customer table has 4 billion records approximatly. Can anyone help please? My best regards