unique keywords_i18n constraint plus delete duplicates (#320)

migrations/000.411.sql

@@ -0,0 +1,18 @@
+-- Add unique keyword_i18n locale constraint
+
+-- First we have to delete the duplicates that already exists (keywords 1316-1326; 138 keywords_i18n entries)
+with duplicates as (
+	select duplicate.id duplicate_id, *
+	from keywords_i18n first
+	-- inner join the same table where keyword_id, locale_id AND value must all be the same,
+	-- i.e. only duplicate translations with the same translated value will be included
+	join keywords_i18n duplicate using (keyword_id, locale_id, value)
+	where first.id <> duplicate.id
+	-- only include the last copy, so we dont delete the original
+	and duplicate.id > first.id
+) delete from keywords_i18n where id in (select duplicate_id from duplicates);
+
+
+-- Now we are allowed to add our constraint
+ALTER TABLE keywords_i18n ADD UNIQUE (keyword_id, locale_id);
+