a test case for double free'ing of pointer in alter table ...

mysql-test/t/temp_table.test

@@ -60,3 +60,8 @@ insert into t2 values (1,1),(2,1),(3,1),(4,2);
 # do a query using ELT, a join and an ORDER BY.
 select one.id, two.val, elt(two.val,'one','two') from t1 one, t2 two where two.id=one.id order by one.id;
 drop table t1,t2;
+create temporary table t1 (a int not null);
+insert into t1 values (1),(1);
+-- error 1062
+alter table t1 add primary key (a);
+drop table t1;