--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/IMPL/SQL/Schema/Constraint/Index.pm	Fri Sep 04 19:40:23 2015 +0300
@@ -0,0 +1,15 @@
+package IMPL::SQL::Schema::Constraint::Index;
+use strict;
+use parent qw(IMPL::SQL::Schema::Constraint);
+
+__PACKAGE__->PassThroughArgs;
+__PACKAGE__->RegisterAlias('index');
+
+sub CTOR {
+    my $this = shift;
+    
+    my %colnames;
+    not grep { $colnames{$_}++ } $this->columns or die new Exception('Each column in the index can occur only once');
+}
+
+1;