Comment 0 for bug 1545129

Setup
=====

DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (
  id tinyint unsigned auto_increment primary key,
  notunique varchar(200) NOT NULL
);
INSERT INTO t1(notunique) VALUES('test01'),('test01'),('test02');
SELECT * FROM t1;

Action
=====

pt-online-schema-change --alter="ADD UNIQUE INDEX unique_1 (notunique)" --statistics --execute h=127.0.0.1,P=5711,D=test,t=t1,u=msandbox,p=msandbox

Expected/Desired result
===================

The osc aborts because the data for the unique index is not unique

Actual result
==========

On MySQL 5.6 data with duplicate entries are dropped silently
On MySQL 5.7 data with duplicate entries are dropped with a warning 1062 in the stats (probably also for MariaDB 5.5+)

Related
======

https://bugs.launchpad.net/percona-toolkit/+bug/1099836

Suggested fix
===========

- Abort on warning 1062 if possible and/or require a --force-unique flag when adding adding an unique index.
- Don't swap/drop if the original table has less rows than the original table

Versions
=======

- MySQL 5.7.11
- pt-online-schema-change 2.2.16 (git b1ca211)