SQL help please? Concat isn't SQlite friendly, unsure of how to fix using these queries.

1 a)

Pull a list of customer ids with the customers full name, and address, along with combining their city and country together. Be sure to make a space in between these two and make it UPPER CASE.

b) Create a new employee user id by combining the first 4 letters of the employees first name with the first 2 letters of the employees last name. Make the new field lower case and pull each individual step to show your work.

c) Show a list of employees who have worked for the company for 15 or more years using the current date function. Sort by lastname ascending.

d) Create a new customer invoice id by combining a customers invoice id with their first and last name while ordering your query in the following order: firstname, lastname, and invoiceID.

e) Which columns from the Customers table contain nul values