Patch file patch_61_62_c.sql adds unique index to db_name field in external_db table.

sql/patch_61_62_c.sql

+# patch_61_62_c.sql
+#
+# Title: Index for db_name.
+#
+# Description:
+# Add unique index to db_name field in external_db table.
+
+CREATE UNIQUE INDEX db_name_idx ON external_db(db_name);
+
+# Patch identifier
+INSERT INTO meta (species_id, meta_key, meta_value)
+  VALUES (NULL, 'patch', 'patch_61_62_c.sql|db_name_idx');