Question

I have two tables countries, location whose fields are

_countries
    countryid(Primary Key)
    countryname

_location
    locationid(primarykey)
    locationname
    countryid(Foreign key from countries table)

Every thing is done using JavaScript,AJAX and php that when a user selects a country from drop down list, locations against each country will be displaced but the mysql query is not working
I am Using the Below Query

$sql="SELECT _location.locationname, _countries.countryname FROM _location 
INNER JOIN _countries ON _location.countryid='".$q."'";

//$q is the countryid selected from drop down list i got it through javascript and php

The drop down list is populated from the countries table
My Question is when a user selects a country name from the drop down list what will be
the mysql query that fetch the location name against each country name and display data like this

||Location name||Country Name||
  Islamabad       Pakistan
  Karachi         Pakistan

Answer 1

 $sql = "SELECT l.locationname, c.countryname
FROM
_countries c
LEFT JOIN _location l ON c.countryid = l.countryid
WHERE c.countryid = ".(int)$q;