> Le 4 févr. 2017 à 21:23, Jeffrey Kain <[email protected]> a écrit : > > In older versions of 4D it was possible to create a field with 'unique' but > not indexed. This causes 4D to have to do full table scans for every > insert/update in order to validate uniqueness. In a large table, this is a > huge performance problem. Clearly a competent developer who understands the > basics of how databases work would never do this on a large, frequently > updated table, but 4D still let you fall into that trap.
Hi Jeffrey, that was not my question, I understand the performance problem and that 4D has to index a field to ensure it's unique with decent speed (although in small tables it seems a bit excessive). Reading indexes in system tables I was surprised first to find 2 UNIQUENESS columns, in field and index. Thinking better, I guess field.unique is just a kind of trigger to create an index.unique. Then I said myself "well, if the index has a uniqueness column, I should be able to set that somewhere". But uniqueness is missing in the create index dialog. It seems index.unique can only be inherited form field.unique or from a primary key definition. -- Arnaud de Montard ********************************************************************** 4D Internet Users Group (4D iNUG) FAQ: http://lists.4d.com/faqnug.html Archive: http://lists.4d.com/archives.html Options: http://lists.4d.com/mailman/options/4d_tech Unsub: mailto:[email protected] **********************************************************************
