Add unique key to meta_key/meta_value columns in meta table.

sql/patch_45_46_d.sql

+# patch_45_46_d.sql
+#
+# title: Meta unique key
+#
+# description:
+# Add unique key to meta_key/meta_value columns in meta table.
+
+ALTER TABLE meta ADD UNIQUE key_value (meta_key, meta_value);
+
+# patch identifier
+INSERT INTO meta (meta_key, meta_value) VALUES ('patch', 'patch_45_46_d.sql|meta_unique_key');
+
+
+