A query generator is operable to generate a query for retrieving data that satisfy a conditional expression from a database, and/or perform an arbitrary calculation on at least part of the retrieved data. The query generator can receive an input query and analyze the query to ascertain whether it contains a replaceable token. If the query contains a replaceable token, the query generator can replace that token with user input specifying a parameter of the conditional expression and/or the arbitrary calculation, thereby generating an output query for retrieving the data that satisfy the conditional expression and/or performing the arbitrary calculation on the retrieved data.