blocks|key|4178388|text|您可以使用mysql_num_rows()统计返回的行数，并检查从查询中收到了多少行。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4178389|$results+=+mysql_query("SELECT+*+FROM...");
if(mysql_num_rows($results)+>+0+)+{
++++//+Got+some+results
}+else+{
++++//no+rows
}|code-block|syntax|javascript|4178390|但是请注意，如果查询由于无效的SQL或其他原因而失败，则$results将为false，因此您可以这样做：|4178391|if(!$results)+{
++++//+Query+was+invalid
}|4178392|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.mysql-num-rows.php^0|5|G|5|G|0|0|0|S|8|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

You can count the number of returned rows with <a href="http://php.net/manual/en/function.mysql-num-rows.php" rel="nofollow noreferrer"><code>mysql_num_rows()</code></a>, and check how many were received from the query. 

<pre><code>$results = mysql_query("SELECT * FROM...");
if(mysql_num_rows($results) &gt; 0 ) {
 // Got some results
} else {
 //no rows
}
</code></pre>

However note that if the query failed due to an invalid SQL or some other reason, <code>$results</code> will be false, so you can just do:

<pre><code>if(!$results) {
 // Query was invalid
}
</code></pre>

blocks|key|1861797|text|为此，您将使用mysql_num_rows()。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1861798|如果mysql_query()返回FALSE，则意味着查询操作存在actaul问题，而不是没有返回任何行。|1861799|流程是这样的：|1861800|$query+=+"SELECT+*+FROM+wherever";
if+(!$result+=+mysql_query($query))+{
++//+mysql_error()+gives+a+human+readable+string+that+explains+what+went+wrong
++//+You+should+**never**+show+it+in+a+production+environment!
++die('MySQL+Error:+'.mysql_error());
}

if+(!mysql_num_rows($result))+{
++//+There+were+no+results
}+else+{
++//+There+were+some+results
}|code-block|syntax|javascript|1861801|这仅适用于返回数据(SELECT、DESCRIBE等)的查询--如果操作成功，则只执行操作(INSERT、UPDATE、DELETE等)的查询将始终返回TRUE；如果操作失败，则始终返回FALSE。|1861802|从manual|1861803|1861804|表示SELECT、SHOW、DESCRIBE、EXPLAIN和其他返回结果集的语句，mysql_query()在成功时返回资源，在错误时返回FALSE。|blockquote|1861805|1861806|对于其他类型的SQL语句，如INSERT、UPDATE、DELETE、DROP等，mysql_query()在成功时返回TRUE，在出错时返回FALSE。|1861807|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.mysql-num-rows.php|1|http://php.net/manual/en/function.mysql-query.php^0|7|G|7|G|0|0|2|D|H|5|0|0|0|A|6|H|8|1A|6|1H|6|1O|6|24|4|2L|5|0|1|6|1|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|F|3|G|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1K|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1L|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]|$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]|$9|1Z|A|20|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|6|7|21|8|@]|D|@$9|22|A|23|1|24]]|E|$]]|$1|S|3|-4|5|6|7|25|8|@]|D|@]|E|$]]|$1|T|3|U|5|V|7|26|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|27|8|@]|D|@]|E|$]]|$1|X|3|Y|5|6|7|28|8|@]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|29|8|@]|D|@]|E|$]]]|10|$11|$5|12|13|14|E|$15|16]]|17|$5|12|13|14|E|$15|18]]]]

You would use <a href="http://php.net/manual/en/function.mysql-num-rows.php" rel="nofollow noreferrer"><code>mysql_num_rows()</code></a> for this.
If <code>mysql_query()</code> returns <code>FALSE</code>it means there was an actaul problem with the query operation, not that there were no rows returned.
The flow goes something like this:
<pre><code>$query = &quot;SELECT * FROM wherever&quot;;
if (!$result = mysql_query($query)) {
 // mysql_error() gives a human readable string that explains what went wrong
 // You should **never** show it in a production environment!
 die('MySQL Error: '.mysql_error());
}

if (!mysql_num_rows($result)) {
 // There were no results
} else {
 // There were some results
}
</code></pre>
This is only true for queries that return data (<code>SELECT</code>, <code>DESCRIBE</code> etc) - queries that just perform an action (<code>INSERT</code>, <code>UPDATE</code>, <code>DELETE</code> etc) will always return <code>TRUE</code> if the action was successful, or <code>FALSE</code> if it failed.
From the <a href="http://php.net/manual/en/function.mysql-query.php" rel="nofollow noreferrer">manual</a>:
<blockquote>
For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error.
For other type of SQL statements, INSERT, UPDATE, DELETE, DROP, etc, mysql_query() returns TRUE on success or FALSE on error.
</blockquote>

blocks|key|1532797|text|如果没有要返回的记录，mysql_num_rows($resultHandle)将返回0(零)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1532798|entityMap^0|B|T|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

If there are no records to return, <code>mysql_num_rows($resultHandle)</code> would return 0 (zero)

blocks|key|4178546|text|不会，如果您的SELECT查询没有返回任何行，mysql_query也将返回资源(而不是FALSE)。要检查是否没有返回任何行，可以使用一组函数：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4178547|4178548|+http://www.php.net/manual/en/function.mysql-num-rows.php|blockquote|4178549|4178550|http://www.php.net/manual/en/function.mysql-fetch-assoc.php|4178551|...|4178552|entityMap|0|LINK|mutability|MUTABLE|url|http://www.php.net/manual/en/function.mysql-num-rows.php|1^0|7|6|N|B|18|5|0|0|1|1K|0|0|0|0|1N|1|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|14|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|15|8|@]|D|@$9|16|A|17|1|18]]|E|$]]|$1|J|3|-4|5|6|7|19|8|@]|D|@]|E|$]]|$1|K|3|L|5|6|7|1A|8|@]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|M|3|N|5|6|7|1E|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|L]]]]

No, <code>mysql_query</code> will return a resource (not <code>FALSE</code>) also if your <code>SELECT</code> query do not return any rows. To check if no rows have been returned, you can use a bounch of functions:

<blockquote>
 <a href="http://www.php.net/manual/en/function.mysql-num-rows.php" rel="nofollow">http://www.php.net/manual/en/function.mysql-num-rows.php</a> 
 <a href="http://www.php.net/manual/en/function.mysql-fetch-assoc.php" rel="nofollow">http://www.php.net/manual/en/function.mysql-fetch-assoc.php</a> 
 ...
</blockquote>

blocks|key|4178423|text|Manual|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4178424|4178425|表示SELECT、SHOW、DESCRIBE、EXPLAIN和其他返回结果集的语句，mysql_query()在成功时返回资源，在错误时返回FALSE。|blockquote|4178426|4178427|4178428|要检查是否成功，最好使用isset或!empty|style|CODE|4178429|$rs+=+mysql_query("select+1");
if+(!empty($rs)){
++++//everything+ran+fine
}
else{
++++//something+broken
}|code-block|syntax|javascript|4178430|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/function.mysql-query.php^0|0|6|0|0|0|0|0|0|C|5|I|6|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|-4|5|6|7|14|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|15|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|16|8|@]|9|@]|C|$]]|$1|I|3|-4|5|6|7|17|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|18|8|@$A|19|B|1A|L|M]|$A|1B|B|1C|L|M]]|9|@]|C|$]]|$1|N|3|O|5|P|7|1D|8|@]|9|@]|C|$Q|R]]|$1|S|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

<a href="http://php.net/manual/en/function.mysql-query.php" rel="nofollow">Manual</a> 

<blockquote>
 For SELECT, SHOW, DESCRIBE, EXPLAIN and other statements returning resultset, mysql_query() returns a resource on success, or FALSE on error.
</blockquote>

To check if it's success, it might be a good idea to use <code>isset</code> or <code>!empty</code>:

<pre><code>$rs = mysql_query("select 1");
if (!empty($rs)){
 //everything ran fine
}
else{
 //something broken
}
</code></pre>

So I want to do a mysql_query - and I want to tell if a resource is null (that is, was unable to pull any values). Would the query be returned as false if no values were present? Am I reading the documentation right on this?

How to tell if a resource is null?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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所以我想做一个mysql_query --我想知道一个资源是否为空(也就是说，我们不能获取任何值)。如果不存在任何值，查询是否会作为false返回？我读到的文档是正确的吗？

问如何判断资源是否为空？
EN

回答 5

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问如何判断资源是否为空？EN

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问如何判断资源是否为空？
EN