如何使用单个查询列出查询行或显示“无记录" [英] How to list rows for a query or display 'no records' using a single query

问题描述

如何在单个查询中没有返回行的情况下列出查询记录并显示无记录"?

How to list records for a query and to display "no records" when no rows returned using a single query?

当前我正在使用COUNT(*)查询或使用mysql_num_rows()函数；然后另一个查询以不同的结果集列出数据.您能告诉我是否可以通过一个查询来完成相同的工作?

Currently I am using a COUNT(*) query or using mysql_num_rows() function; then another query in different result set to list data. Can you tell me if it is possible to accomplish the same with a single query?

推荐答案

重要提示::我假设OP使用PHP，因为他提到了mysql_num_rows.我希望他能告诉我我是否错了.

Important: I assume that the OP uses PHP as (s)he mentions mysql_num_rows. And I hope (s)he will tell me if I am wrong.

检查结果是否为空集是您在PHP中的工作.我不明白您为什么必须再进行一次查询.也许您必须澄清您的问题.

It is your job in PHP to check whether the result is an empty set or not. I don't understand why you have to do another query. Maybe you have to clarify your question.

这里有一个更完整的示例:

Here a more complete example:

$link = mysql_connect("localhost", "mysql_user", "mysql_password");
mysql_select_db("database", $link);

$result = mysql_query("SELECT * FROM table1", $link);

// If if result set contains rows
if(0 == mysql_num_rows($result)) {
    echo 'no records';
}
else { // Loop over the result set
    while(row = mysql_fetch_array($result)) {
       // do whatever you want with the data here
    }
}

参考: mysql_num_rows ， mysql_fetch_array

即使您不使用PHP，其他语言也是如此，并且应该有类似的功能.

Even if you don't use PHP, the approach is the same in other languages and there should be similar functions available.

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