Error in query1: SELECT author.surname, author.name FROM paper, author_paper, author WHERE paper.cat = author_paper.id_paper AND author_paper.id_author = author.cat AND paper.volume= AND paper.issue= AND paper.php='petrydesova_liscak' ORDER BY author_paper.ord ASC ERROR: syntax error at or near "AND" LINE 1: ...or_paper.id_author = author.cat AND paper.volume= AND paper.... ^