Reject User Pre-Proxy - SQL

[Andrei Antonelli]

Hello,
I would like to reject pre-proxy some specific users by querying the mysql
database.

I've created a table with these users that will be rejected.

In policy.d/filter

This rule worked.

filter_user {
if (&User-Name == 'XXX at XXX') {
                reject
}
}

But I want to query these users in the database.

I tried.

filter_user {
if ("%{sql:SELECT username FROM radcheckblock WHERE username =
'%{User-Name}'}" == &User-Name) {
           reject
}
}

Error:
policy.d/filter[20]: Parse error in condition
policy.d/filter[20]: ("%{sql:SELECT username FROM radcheckblock WHERE
username = '%{User-Name}'}" == &User-Name) {
policy.d/filter[20]:  ^ Cannot use attribute reference on right side of
condition


What would be the best way to do this filter?

thank you all