mysql返回空集 | mysql返回空集

本文介绍了mysql返回空集的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

非常令人沮丧，但 mysql 正在为此代码返回一个空集(不存在回显):

Been very frustrating but mysql is returning an empty set for this code (not echoing exists) :

if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }
  mysql_select_db("repository", $con);

$url = stripslashes($url);
$url = mysql_real_escape_string($url, $con);
$exists = mysql_query("SELECT url FROM sites WHERE url = '$url' LIMIT 1");
 if (mysql_num_rows($exists) == 1) {
    echo "exists";
 }

它不应该这样做，因为我已经测试了很多.

it should not be doing this because I've tested a good amount.

该表由一列url"组成，数据类型为 varchar(1000)(最大值).为测试目的存储的 url 是 http://en.wikipedia.org/wiki/Thailand

The table consists of one column "url", it is datatype varchar(1000) (the maximum). the url stored for test purposes is http://en.wikipedia.org/wiki/Thailand

推荐答案

这是您的第一步.从查询中完全删除 WHERE url = '$url' 并在使用它之前打印出 mysql_num_rows($exists).

Here's what you do as a first step. Remove the WHERE url = '$url' from your query altogether and print out mysql_num_rows($exists) before using it.

这应该足以说明它是否是两个最可能的问题之一:

That should be enough to tell if it's one of the two likeliest problems:

错误的 URL 导致没有返回任何行；或
由于数据库包含非预期内容而导致的错误行.

根据您迄今为止的评论，前者的可能性最大.如果结果证明您在没有where 子句的情况下返回了一行，则您必须弄清楚为什么您的 URL 不正确.这可能是区分大小写的问题或填充(大小)问题等.

Based on your comments to date, the former is the most likely. If it turns out you get a row back without the where clause, you'll have to figure out why your URL is incorrect. This may be a case-sensitivity issue or a padding (size) issue, among other things.

如果，正如您在评论中提到的，like 在 = 不起作用的地方起作用，那么我们需要查看您的数据.

If, as you mention in a comment, like works where = doesn't, then we need to see your data.

执行(在数据库级别):

Execute (at the DB level):

select concat('[',url,']') from sites

并向我们展示确切的输出是什么.类似地，输出代码使用的 URL，例如:

and show us exactly what the output is. Similarly, output the URL being used by the code with something like:

print_r($url)

紧接在执行 mysql_query 之前.

请将这两个命令的输出附加到您的问题中.

Please append the output from both those commands to your question.

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