您必须将选择标记包装到表单标记中。

 < form action =''method ='post'> 
< select name =myselectbox> 
< option name =myoption1value =myoption1> myoption1< / option> 
< option name =myoption2value =myoption2> myoption2< / option> 
< option name =myoption3value =myoption3> myoption3< / option> 
< option name =myoption4value =myoption4> myoption4< / option> 
< / select> 
< input type ='submit'value ='submit'/> 
< / form> 
 

一旦您提交表单，您将获得后变量为 $ _ POST ['myselectbox'] 可以像你已经做的那样附加到mysql查询中。但为更好的方式不只是追加它，但检查表单提交和后附加变量是否可用。
例如：

  if（！empty（$ _ POST ['myselectbox']））{
 / * ...做你的查询部分... * / 
} 
 

I want to insert the value of a selected 'select form' into my mysql database.

How can i get the right value of this?

<form action='' method='post'>
 <select name="myselectbox">
  <option name="myoption1" value="myoption1">myoption1</option>
  <option name="myoption2" value="myoption2">myoption2</option>
  <option name="myoption3" value="myoption3">myoption3</option>
  <option name="myoption4" value="myoption4">myoption4</option>
 </select>
<input type='submit' value='submit'/>
</form>

something like that? (this one didn't work obviously..)

$sql = "INSERT INTO Entries (myoption1) VALUES ('$_POST[myselectbox]')";

you have to wrap your select tag into a form tag .

<form action='' method='post'>
<select name="myselectbox">
   <option name="myoption1" value="myoption1">myoption1</option>
   <option name="myoption2" value="myoption2">myoption2</option>
   <option name="myoption3" value="myoption3">myoption3</option>
   <option name="myoption4" value="myoption4">myoption4</option>
</select>
<input type='submit' value='submit'/>
</form>

once you submit the form, you will get the post variable as $_POST['myselectbox'] that could be appended into a mysql query as you have already did. but for a better way dont just append it like that but check the form is submitted and post variables are available or not before appending. eg:

if(!empty($_POST['myselectbox'])){
    /*.. do your query section... */
}