Error with data replacement ( REPLACE) in SQLite

Question

SQLite

Task: it is necessary to populate the SQLite database through the fmdb framework in xcode. If data is available, then simply replace them.
Error in this place. The data is not replaced, but simply added to the database, i.e. are duplicated. Where is the mistake?
[database executeUpdate:@"REPLACE INTO list (free, image,title,id,author) VALUES (:free, :img, :title, :id, :author_title)" withParameterDictionary:theCourse];

Answer 1

What fields determine the uniqueness of data?
Most likely there is no unique-index on key fields.