public static <T extends Number> WindowOver<T> avg(Expression<T> expr) {
        return new WindowOver<T>(expr.getType(), Ops.AggOps.AVG_AGG, expr);
    }
Start a window function expression

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