选择元素对

Question

好吧，我有一张桌子上有一份电脑列表，还有他们的速度和内存。如何进行查询以检索具有相同速度和RAM的所有计算机对作为示例？我只能显示一对，所以（i，j）代替（i，j）和（j，i）

类似的东西：

<select>
  <script type="text/javascript">
  var $year = new Date().getFullYear() - 2000;
  var test = '';

  if(test > 2000) {
    // This never happens
    test = test - 2000;
  }

  for(var i=0; i<10; i++) {
    var selected = "";

    if(test == '') {
      // This always happens as test is ''
      if(i == 2) { selected = "selected"; }
    } else {
      // This never happens
      if(i+$year == test) { selected = "selected"; }
    }

    document.write("<option value='"+(i+$year)+"' "+ selected +">"+ (i+$year) +"</option>");
  }
  </script>
</select>

所以par将是1006和1007

Answer 1

这是一个自我加入：

select c.model, c2.model, c.speed, c.ram
from computers c join
     computers c2
     on c.speed = c2.speed and c.ram = c2.ram and c.model < c2.model;