public static <T> WindowOver<T> firstValue(Expression<T> expr) {
        return new WindowOver<T>(expr.getType(), SQLOps.FIRSTVALUE, expr);
    }
returns value evaluated at the row that is the first row of the window frame

@param expr argument
@return first_value(expr)
querydsl-sql/src/main/java/com/querydsl/sql/SQLExpressions.java