(1) In the DDS for a join logical file, the first physical file specified on the JFILE keyword. See also secondary file.
(2) For certain types of join operations using Query, the first of all files that are joined in a query definition. The data from this file is used in every record formed by a join specification.
(3) In RPG, if specified, the first file from which RPG reads a record. In multifile processing, the primary file is used to determine whether the MR indicator is set on. See also full procedural file.