Abstract: A method of generating a SQL statement for retrieving a data set from a database via a user interface and a database server and then processing the data set recursively. The method comprises the following steps: a) inputting a nested n-pass expression to the user interface in a form that the database server cannot execute; and b) converting the nested n-pass expression into a SQL statement that the database server can execute, the SQL statement having a level of recursion for each level of nesting of the n-pass expression, each level of recursion operating in use on the results of at least one of the preceding levels.