Question

我正在将Node.js与mysql模块一起使用，并试图找出如何在两个用户共享类似标签的表中搜索所有实例。我的表的快速演示将是：

username | tag
-------------------
jennifer | coffee
jennifer | pizza
jennifer | travel
joe      | sushi
joe      | bowling
joe      | coffee
joe      | travel
celine   | singing
celine   | pizza
celine   | programming

因此，例如，我想找到乔和珍妮弗共有的标签，在这种情况下，这两个标签是两个：咖啡和旅行。搜索他们共有的标签的最佳方法是什么？任何意见将是有益的。提前谢谢！

Answer 1

这将找到提供2个名称的常用标签：

SELECT tag
FROM yourTable
WHERE username in ("jennifer", "joe")
GROUP BY tag
HAVING count(*) > 1

Answer 2

应该足够简单：

connection.query('SELECT username, tag from my_table where user="joe" or user="jennifer"', function(err, rows, fields) {
  if (err) throw err;

  // Reduce results to a list of Joe's tags
  const joesTags = rows.filter(function(row) {
    return row.username === 'joe';
  }).map(function (row) {
    return row.tag;
  });

  // Determine common tags by filtering to tags of Jennifer's that are also in Joe's list
  const commonTags = rows.filter(function(row) {
    return row.username === 'jennifer' && joesTags.indexOf(row.tag) !== -1
  });
});

我确信这不是最有效的方法，但它应该有用。

利用ES6语法（需要Node 4.x或更高版本）的Terser示例：

connection.query('SELECT username, tag from my_table where user="joe" or user="jennifer"', function(err, rows, fields) {
  if (err) throw err;

  // Reduce results to a list of Joe's tags
  const joesTags = rows.filter(row => row.username === 'joe').map(row => row.tag);

  // Determine common tags by filtering to tags of Jennifer's that are also in Joe's list
  const commonTags = rows.filter(row => row.username === 'jennifer' && joesTags.indexOf(row.tag) !== -1);
});

如何在两行之间搜索共享列值？

2 个答案: