Question

I’ll try to explain this the best I can.

I have a drop down populated with country names from one table. When someone selects say Canada, I need a second dropdown to filter the results from a second table called regions.

Here is the code I’m using

<?php
$query="SELECT * FROM location_region";

$result = mysql_query ($query);
echo "<select id='province_select' name='province_select' class='province_select' style='width:540px' value=''></option>";

while($nt=mysql_fetch_array($result)){
echo "<option value=$nt[value]>$nt[name]</option>"

}
echo "</select>";
?>

I know I have to change the Query, but can I do something like:

$query="SELECT * FROM location_region WHERE country EQUALS value FROM location_country";

This doesn’t work, but is there another where of writing this? The table
“location_region” has a column named “country” that should be equal to the column “value” from the table “location_country”

Thanks as always

EDIT: For Gershon Herczeg here is the table structure

location_country is something similar to:

ID name          value
1  Canada        CA 
2  Great Britain GB
3  United States US

location_region is similar to:

ID name             value  country
1  Alberta          AB     CA
2  Alabama          AL     US
3  British Columbia BC     CA

Answer 1

Yes, this is called an inner join – it’ll effectively give you one big collection of rows matched on a column or columns specified.

SELECT lr.* 
FROM location_region lr
INNER JOIN location_country lc on lr.country = lc.country
WHERE lr.country = <selected value from dropdown>

Replacing in the selected value into the query, this should give you everything from the regions table for the country you’ve selected.

However, if you have a country column in the regions table which matches values in your dropdown, why don’t you just select from that to begin with?

SELECT * 
FROM location_region 
WHERE country = <selected value from dropdown>