<query id="getAttachedFileSize" action="select">
    <tables>
        <table name="files" />
    </tables>
    <columns>
        <column name="sum(file_size)" alias="attached_size" />
    </columns>
    <conditions>
        <condition operation="equal" column="upload_target_srl" var="upload_target_srl" filter="number" notnull="notnull" />
    </conditions>
</query>
