add release note, remote truncate

doc/release-notes/9983-unique-constraints.md

@@ -0,0 +1,9 @@
+This release adds two missing database constraints that will assure that the externalvocabularyvalue table only has one entry for each uri and that the oaiset table only has one set for each spec. (In the very unlikely case that your existing database has duplicate entries now, install would fail. This can be checked by running
+
+SELECT uri, count(*) FROM externalvocabularyvaluet group by uri;
+
+and
+
+SELECT spec, count(*) FROM oaiset group by spec;
+
+and then removing any duplicate rows (where count>1).

src/main/resources/db/migration/V6.0.0.2__9983-missing-unique-constraints.sql

@@ -2,7 +2,6 @@ DO $$
 BEGIN
 
   BEGIN
-    TRUNCATE externalvocabularyvalue
     ALTER TABLE externalvocabularyvalue ADD CONSTRAINT externalvocabularvalue_uri_key UNIQUE(uri);
   EXCEPTION
     WHEN duplicate_table THEN RAISE NOTICE 'Table unique constraint externalvocabularvalue_uri_key already exists';