added back relation filter reference support

tools/dbutils/index.go

@@ -192,3 +192,16 @@ func ParseIndex(createIndexExpr string) Index {
 
 	return result
 }
+
+// HasColumnUniqueIndex loosely checks whether the specified column has
+// a single column unique index (WHERE statements are ignored).
+func HasSingleColumnUniqueIndex(column string, indexes []string) bool {
+	for _, idx := range indexes {
+		parsed := ParseIndex(idx)
+		if parsed.Unique && len(parsed.Columns) == 1 && strings.EqualFold(parsed.Columns[0].Name, column) {
+			return true
+		}
+	}
+
+	return false
+}