@Override
    public String toString() {
        return "CompiledField{" +
                "column=" + column +
                ", groupDepth=" + groupDepth +
                ", generator=" + generator +
                '}';
    }
If the function selects a child row return true.

@return True is the function selects a child row.
stroom-query/stroom-query-common/src/main/java/stroom/query/common/v2/CompiledColumn.java