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

Question

I discovered numerous views with an order by 1 clause when browsing through some outdated code at work. What is the result of this?

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

This:

ORDER BY 1

...is referred to as an "Ordinal" since the number designates the column depending on how many columns are specified in the SELECT clause. According to the question you gave, it means:

ORDER BY A.PAYMENT_DATE

It's not a recommended practice, because:

1. It's not obvious/explicit
2. If the column order changes, the query is still valid so you risk ordering by something you didn't intend

I hope this helps you.