How can I use the custom field id in a query?

[Martin]

I have a custom field which is a dropdown where I have a list, once I make the selection of an item from that drop, what I need is that in another dropdown, show me just the childreen of the first selection.

I'm using nFeed for the configuration of the querys that I need for extracting the first list, in theory I already have the query for just extract the childreen, but what I dont know is how to actually use what is in the fisrt field so it can make the correct extraction of the information that I need for the second field.

PD: I cant use static data because each item on the first field has it own and different childreen

[Mohamed Benziane]

Hello,

The parent list have a null value in customfieldoption in the database, and the child have a value (e.g 11700).

select customvalue from customfieldoption cfo join customfieldvalue cfv ON 
cfo.customfield = cfv.customfield 
and cfo.id = cast(cfv.STRINGVALUE as decimal) 
where cfo.customfield=11702
and cfo.parentoptionid ISNULL

 This query will select you only the parent option