Read SQL Queries only once on app start

Opening the file everytime the query is needed needs more time and the current implementation (without file#close) is not good. (https://stackoverflow.com/a/25070939/15496269)

You could maybe add a class, that reads the sql files, with the different SQL Queries as static attributes. The DB Queries can also be abstracted more with a method for each query that is given the required parameters.