It is generally used for stand-alone lists. When files must be related (customers to orders, vendors to purchases, etc.), a relational database manager is used, not a flat file manager.

SQL statements are used both for interactive queries for information from a relational database and for gathering data for reports. There are a number of database categories, from basic flat files ...

In non-relational "hierarchical" and "network" databases, records in one file contain embedded pointers to the locations of records in another, such as customers to orders and vendors to purchases.

For example, SSIS is perfectly suited for importing a "flat file," such as a CSV, into a relational database. Using SSIS's graphical designer, the task is straightforward, if not entirely intuitive.