Fixed bug#16861: User defined variable can have a wrong value if a tmp table was

used.

Sorting by RAND() uses a temporary table in order to get a correct results.
User defined variable was set during filling the temporary table and later
on it is substituted for its value from the temporary table. Due to this
it contains the last value stored in the temporary table.

Now if the result_field is set for the Item_func_set_user_var object it 
updates variable from the result_field value when being sent to a client.

The Item_func_set_user_var::check() now accepts a use_result_field
parameter. Depending on its value the result_field or the args[0] is used
to get current value.

1 files changed, 10 insertions, 0 deletions

diff --git a/mysql-test/t/user_var.test b/mysql-test/t/user_var.test
index 58c52b59a5a..b2a9728de00 100644
--- a/mysql-test/t/user_var.test
+++ b/mysql-test/t/user_var.test
@@ -202,3 +202,13 @@ SET @a := (select * from bigfailure where afield = (SELECT afield FROM bigfailur
 SELECT @a;
 
 drop table bigfailure;
+
+#
+# Bug#16861: User defined variable can have a wrong value if a tmp table was
+#            used.
+#
+create table t1(f1 int, f2 int);
+insert into t1 values (1,2),(2,3),(3,1);
+select @var:=f2 from t1 group by f1 order by f2 desc limit 1;
+select @var;
+drop table t1;