php - 期望多个结果时正确的 SELECT 查询

Question

我正在尝试为我的问题提出正确的查询。基本上，如果我这样做的话，我可能会得到超过 100 个完全相同的结果:

    $query = "SELECT * FROM highway WHERE state  = 'VA'";
    $result = mysql_query($query) or die(mysql_error());
    while ($row = mysql_fetch_array($result)) {
    //code

有了这个我会得到:

    95
    95
    95
    95 (and on and on...)
    64
    64
    64 (and on and on...)

要获取的正确查询是什么:

    95
    64
    66
    81

Answer 1

您可以使用DISTINCT关键字:

The ALL and DISTINCT options specify whether duplicate rows should be returned. ALL (the default) specifies that all matching rows should be returned, including duplicates. DISTINCT specifies removal of duplicate rows from the result set. It is an error to specify both options. DISTINCTROW is a synonym for DISTINCT.

所以:

SELECT DISTINCT * FROM highway WHERE state  = 'VA'

但是，如果您的结果集在考虑某些列时有重复项，那么在我看来，您的数据库表可能设计得很糟糕。您是否进一步考虑过normalising他们？