What is the purpose of Order By 1 in SQL select statement?

Question

I'm reading through some old code at work, and have noticed that there are several views with an order by 1 clause. What does this accomplish?

Example:

Create view v_payment_summary AS

SELECT A.PAYMENT_DATE,

       (SELECT SUM(paymentamount)

          FROM payment B

         WHERE PAYMENT_DATE = B.PAYMENT_DATE

           and SOME CONDITION) AS SUM_X,

       (SELECT SUM(paymentamount)

          FROM payment B

         WHERE PAYMENT_DATE = B.PAYMENT_DATE

           and SOME OTHER CONDITION) AS SUM_Y    

FROM payment A    

ORDER BY 1;

Answer 1

ORDER BY 1 

The above syntax is known as an "Ordinal" - Here, the number stands for the column based on the number of columns defined in the SELECT clause. 

In the query that you have provided, it means:

ORDER BY A.PAYMENT_DATE

It's not recommended to use, because it's not explicit/obvious. But, if the column order changes, then the query will be valid.