title: why did this mysql table copy generate duplicate rows
body: <p>I did </p>
  
  <pre><code>insert  t1  select *  from  t2;
  </code></pre>
  
  <p>to copy a table, after creating t1 by </p>
  
  <pre><code>CREATE TABLE t1 (
    `c` text COLLATE utf8_unicode_ci,
    `d` text COLLATE utf8_unicode_ci,
    `count` int(11) DEFAULT NULL,
    `d1` double DEFAULT NULL,
    `d2` int(11) DEFAULT NULL,
    `c1` double DEFAULT NULL,
    `c2` int(11) DEFAULT NULL
  ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
  </code></pre>
  
  <p>A count of original and duplicate tables shows 69M vs. 80M rows , and indeed I see duplicate rows in the copied table - does someone know why this can happen?  The original table was innodb and copy is myisam, perhaps this is the source of the dupication?</p>