blocks|key|865340|text|一种方法是检查mysql_num_rows返回的内容。一个最小的完整示例如下：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|865341|if+($result+=+mysql_query($sql)+&&+mysql_num_rows($result)+>+0)+{
++++//+there+are+results+in+$result
}+else+{
++++//+no+results
}|code-block|syntax|javascript|865342|但建议您检查mysql_query的返回值，并在返回值为false+(这可能是由错误引起的)的情况下正确处理它；可能还需要调用mysql_error并将错误记录在某个地方。|865343|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/it/function.mysql-num-rows.php|1|http://php.net/manual/en/function.mysql-query.php|2|http://php.net/manual/en/function.mysql-error.php^0|7|E|7|E|0|0|0|6|B|S|5|1R|B|6|B|1|1R|B|2|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@$9|1C|A|1D|1|1E]|$9|1F|A|1G|1|1H]]|E|$]]|$1|M|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]|W|$5|P|Q|R|E|$S|X]]]]

One way to do it is to check what <a href="http://php.net/manual/it/function.mysql-num-rows.php" rel="noreferrer"><code>mysql_num_rows</code></a> returns. A minimal complete example would be the following: 

<pre><code>if ($result = mysql_query($sql) &amp;&amp; mysql_num_rows($result) &gt; 0) {
 // there are results in $result
} else {
 // no results
}
</code></pre>

But it's recommended that you check the return value of <a href="http://php.net/manual/en/function.mysql-query.php" rel="noreferrer"><code>mysql_query</code></a> and handle it properly in the case it's <code>false</code> (which would be caused by an error); probably by also calling <a href="http://php.net/manual/en/function.mysql-error.php" rel="noreferrer"><code>mysql_error</code></a> and logging the error somewhere.

blocks|key|1080051|text|使用带有mysql_fetch_row的语句，因为“对于返回结果集的SELECT、SHOW、DESCRIBE、EXPLAIN和其他语句，mysql_query()在成功时返回资源，在错误时返回FALSE。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1080052|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。“|1080053|entityMap^0|4|F|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|N|8|@]|D|@]|E|$]]]|I|$]]

Use the one with <code>mysql_fetch_row</code> because "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. "

blocks|key|1080090|text|在上面的所有选项中，我将使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1080091|if+(mysql_num_rows($result)==0)+{+PERFORM+ACTION+}|offset|length|style|CODE|1080092|对照如下结果进行检查|1080093|if+(!$result)+{+PERFORM+ACTION+}|code-block|syntax|javascript|1080094|如果mysql_error发生得如此有效，这将是正确的。如果发生错误，则可以输入重复的用户名...|1080095|entityMap^0|0|0|1E|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|X|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Of all the options above I would use 

<code>if (mysql_num_rows($result)==0) { PERFORM ACTION }</code> 

checking against the result like below

<pre><code>if (!$result) { PERFORM ACTION }
</code></pre>

This will be true if a mysql_error occurs so effectively if an error occurred you could then enter a duplicate user-name...

blocks|key|1080145|text|我通常使用===+(triple+equals)和__LINE__，__CLASS__来定位代码中的错误：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1080146|$query=mysql_query('SELECT+champ+FROM+table')
or+die("SQL+Error+line++".__LINE__+."+class+".__CLASS__."+:+".mysql_error());

mysql_close();

if(mysql_num_rows($query)===0)
{
++++PERFORM+ACTION;
}
else
{
++++while($r=mysql_fetch_row($query))
++++{
++++++++++PERFORM+ACTION;
++++}
}|code-block|syntax|javascript|1080147|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/80646/how-do-the-equality-double-equals-and-identity-triple-equals-compariso^0|5|3|P|8|Y|9|A|D|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$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]]|$1|K|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

Usually I use the <code>===</code> (<a href="https://stackoverflow.com/questions/80646/how-do-the-equality-double-equals-and-identity-triple-equals-compariso">triple equals</a>) and <code>__LINE__</code> , <code>__CLASS__</code> to locate the error in my code:

<pre><code>$query=mysql_query('SELECT champ FROM table')
or die("SQL Error line ".__LINE__ ." class ".__CLASS__." : ".mysql_error());

mysql_close();

if(mysql_num_rows($query)===0)
{
 PERFORM ACTION;
}
else
{
 while($r=mysql_fetch_row($query))
 {
 PERFORM ACTION;
 }
}
</code></pre>

blocks|key|1080249|text|每当我们进行查询以获取某些数据时，它都会以对象的形式返回。然后，我们大多数人都会将其转换为数组，以便轻松地遍历各行。在php中，"+empty+()“函数用于检查数组是否为空，即该数组中是否没有数据。因此我们可以检查查询返回的数组表示是否为空，如下所示|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1080250|if(!empty($result)){
+++++++++++//DO+STUFF
}|code-block|syntax|javascript|1080251|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Whenever we do queries to get some data, it is returned as an object. Then most of us convert it to array for looping through the rows easily. In php "empty()" function is used to check if an array is empty i.e. if it has no data in it. So we can check if returned array representation of query isn't empty by doing like this

<pre><code>if(!empty($result)){
 //DO STUFF
}
</code></pre>

blocks|key|865707|text|比在处理前测试结果变量的类型更符合逻辑的是什么？它是'boolean‘或'resource’类型。当您在mysqli_num_rows中使用参数的布尔值时，将会生成警告，因为该函数需要一个资源。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|865708|$result+=+mysqli_query($dbs,+$sql);

if(gettype($result)=='boolean'){+//+test+for+boolean
++++if($result){++//+returned+TRUE,+e.g.+in+case+of+a+DELETE+sql++
++++++++echo+"SQL+succeeded";+
++++}+else+{+//+returned+FALSE
++++++++echo+"Error:+"+.+mysqli_error($dbs);
++++}+
}+else+{+//+must+be+a+resource
++++if(mysqli_num_rows($result)){

+++++++//+process+the+data++++

++++}
++++mysqli_free_result($result);++
+}|code-block|syntax|javascript|865709|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

What is more logical then testing the TYPE of the result variable before processing?
It is either of type 'boolean' or 'resource'. When you use a boolean for parameter with mysqli_num_rows, a warning will be generated because the function expects a resource. 

<pre><code>$result = mysqli_query($dbs, $sql);

if(gettype($result)=='boolean'){ // test for boolean
 if($result){ // returned TRUE, e.g. in case of a DELETE sql 
 echo "SQL succeeded"; 
 } else { // returned FALSE
 echo "Error: " . mysqli_error($dbs);
 } 
} else { // must be a resource
 if(mysqli_num_rows($result)){

 // process the data 

 }
 mysqli_free_result($result); 
 }
</code></pre>

blocks|key|865777|text|$result+=+$mysqli->query($query);
if($result){
++++perform+action
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|865778|这就是我怎么做的，你也可以在那里扔一个骰子…|unstyled|865779|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>$result = $mysqli-&gt;query($query);
if($result){
 perform action
}
</code></pre>

this is how i do it, you could also throw an else there with a die...

blocks|key|1080478|text|如果$result无效，您仍要执行该操作：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1080479|if(!mysql_num_rows($result))
++++//+Do+stuff|code-block|syntax|javascript|1080480|这将说明失败时由mysql_num_rows()返回的0和false。|1080481|entityMap^0|2|7|0|0|8|G|R|1|T|5|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

If you would still like to perform the action if the <code>$result</code> is invalid: 

<pre><code>if(!mysql_num_rows($result))
 // Do stuff
</code></pre>

This will account for a <code>0</code> and the <code>false</code> that is returned by <code>mysql_num_rows()</code> on failure.

blocks|key|865925|text|如果没有行，则mysqli_fetch_array()返回NULL。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|865926|在过程式风格中：|865927|if+(+!+$row+=+mysqli_fetch_array(+$result+)+)+{
++++...+no+result+...
}
else+{
++++...+get+the+first+result+in+$row+...
}|code-block|syntax|javascript|865928|在面向对象的风格中：|865929|if+(+!+$row+=+$result->fetch_array()+)+{
++++...
}
else+{
++++...+get+the+first+result+in+$row+...
}|865930|entityMap^0|7|K|T|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|10|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|R|$]]

<code>mysqli_fetch_array()</code> returns <code>NULL</code> if there is no row.

In procedural style: 

<pre><code>if ( ! $row = mysqli_fetch_array( $result ) ) {
 ... no result ...
}
else {
 ... get the first result in $row ...
}
</code></pre>

In Object oriented style:

<pre><code>if ( ! $row = $result-&gt;fetch_array() ) {
 ...
}
else {
 ... get the first result in $row ...
}
</code></pre>

blocks|key|1080550|text|$connect+=+new+mysqli('localhost',+'user',+'password',+'db');
$result+=+$connect->query("select+*+from+...");
$count=$result->num_rows;
if(empty($count)){
echo"Query+returned+nothing";
}
else{
echo"query+returned+results";
}+|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1080551|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>$connect = new mysqli('localhost', 'user', 'password', 'db');
$result = $connect-&gt;query("select * from ...");
$count=$result-&gt;num_rows;
if(empty($count)){
echo"Query returned nothing";
}
else{
echo"query returned results";
} 
</code></pre>

I'm looking for the best way to check and see if any results were returned in a query. I feel like I write this part of code a lot and sometimes I get errors, and sometimes I don't.

For example, I run this query to check if a username exists before inserting a new one into the database.

<pre><code>$result = mysql_query("SELECT * FROM ...");
</code></pre>

Then I want to check and see if any results were returned. Here is one way I do it:

<pre><code>if (!$result) { PERFORM ACTION }
</code></pre>

If the first way doesn't work, then sometimes this will:

<pre><code>if (mysql_num_rows($result)==0) { PERFORM ACTION }
</code></pre>

Then I even saw that I could do it this way the other day:

<pre><code>list($total) = mysql_fetch_row($result);
if ($total==0) { PERFORM ACTION }
</code></pre>

What is the best way to do this?

Best way to check if mysql_query returned any results?

数据库

我正在寻找最好的方法来检查并查看查询中是否返回了任何结果。我觉得我写了很多这部分代码，有时会出错，有时不会。例如，在将新用户名插入数据库之前，我运行此查询来检查用户名是否存在。$result = mysql_query("SELECT * FROM ...");然后我想检查并查看是否返回了任何结果。下面是我的一种方法：...

问检查mysql_query是否返回任何结果的最好方法？
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问检查mysql_query是否返回任何结果的最好方法？
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