Due to a bug in MySQL we need to drop the unique index, change the field to...

Due to a bug in MySQL we need to drop the unique index, change the field to varchar then reaply the index otherwise latin1 encodings can cause a constraint error to occur. This only affects the conversion of enum to varchar

sql/patch_63_64_d.sql

@@ -7,10 +7,14 @@
 #    Change the column definition to VARCHAR(3) instead of providing
 #    a list of allowable values. Values will be tested in healthchecks.
 
+ALTER TABLE ontology_xref DROP INDEX object_source_type_idx;
 
 ALTER TABLE ontology_xref
   MODIFY linkage_type VARCHAR(3) DEFAULT NULL;
 
+ALTER TABLE ontology_xref 
+  ADD UNIQUE INDEX object_source_type_idx (object_xref_id, source_xref_id, linkage_type);
+
 # Insert patch identifier.
 INSERT INTO meta (species_id, meta_key, meta_value)
   VALUES (NULL, 'patch',