Bug #16494: Updates that set a column to NULL fail sometimes

 When building the UPDATE query to send to the remote server, the
 federated storage engine built the query incorrectly if it was updating
 a field to be NULL.

 Thanks to Bjšrn Steinbrink for an initial patch for the problem.


mysql-test/r/federated.result:
  Add new results
mysql-test/t/federated.test:
  Add new regression test
sql/ha_federated.cc:
  Fix logic of how fields are added to SET and WHERE clauses of an
  UPDATE statement. Fields that were NULL were being handled incorrectly.
  Also reorganizes the code a little bit so the update of the two
  clauses is consistent.

1 files changed, 17 insertions, 0 deletions

diff --git a/mysql-test/t/federated.test b/mysql-test/t/federated.test
index 80b31c610a2..d24caf1aa08 100644
--- a/mysql-test/t/federated.test
+++ b/mysql-test/t/federated.test
@@ -1309,5 +1309,22 @@ DROP TABLE federated.t1;
 connection slave;
 DROP TABLE federated.bug_17377_table;
 
+#
+# Bug #16494: Updates that set a column to NULL fail sometimes
+#
+connection slave;
+create table t1 (id int not null auto_increment primary key, val int);
+connection master;
+eval create table t1
+  (id int not null auto_increment primary key, val int) engine=federated
+  connection='mysql://root@127.0.0.1:$SLAVE_MYPORT/test/t1';
+insert into t1 values (1,0),(2,0);
+update t1 set val = NULL where id = 1;
+select * from t1;
+connection slave;
+select * from t1;
+drop table t1;
+connection master;
+drop table t1;
 
 source include/federated_cleanup.inc;