title: Mybatis mapper list return the result repetition
body: <p>I want to use list put into query result,database have two data,but there are four results in the list.,why this repeat  query</p>
  <pre><code>    &lt;select id=&quot;selectList&quot; resultType=&quot;map&quot; &gt;
          &lt;foreach collection=&quot;list&quot; item=&quot;items&quot; separator=&quot; union all &quot;&gt;
              SELECT
              #{items.id,jdbcType=INTEGER} id,
              #{items.name,jdbcType=VARCHAR} name
              FROM category
          &lt;/foreach&gt;
      &lt;/select&gt;
  </code></pre>
  <pre><code>    public void selectList() {
          Map&lt;String, Object&gt; map1 = new HashMap&lt;&gt;();
          map1.put(&quot;name&quot;, &quot;haha&quot;);
          map1.put(&quot;id&quot;, &quot;1&quot;);
  
          Map&lt;String, Object&gt; map2 = new HashMap&lt;&gt;();
          map2.put(&quot;name&quot;, &quot;update&quot;);
          map2.put(&quot;id&quot;, &quot;2&quot;);
  
          List&lt;Map&lt;String, Object&gt;&gt; list = new ArrayList&lt;&gt;();
          list.add(map1);
          list.add(map2);
  
          List&lt;Map&lt;String, Object&gt;&gt; resultList = categoryDao.selectList(list);
          for (Map&lt;String,Object&gt; m : resultList){
              System.out.println(m.toString());
          }
      }
  
  }
  </code></pre>
  <p><img src="https://i.stack.imgur.com/mpQLM.png" alt="enter image description here" /></p>
  <p><img src="https://i.stack.imgur.com/9aNBg.png" alt="enter image description here" /></p>
  <p>Why there are four here?</p>