How to assign a result of sqltask to variable

Hi All

How to assign a result of sqltask to variable

E.g.

Lets say i have this in my build.xml

<sql
    driver="oracle.jdbc.driver.OracleDrive"
    url="jdbc:database-url"

    userid="sa"
    password="pass"
    >
SELECT user_id FROM user where user_name=${user.name};
</sql>

in this how do i assign user_id now to any variable,?

Please help