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Oracle optimizer Or Expansion Transformations

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The previous installment of this series examined aggregate subquery removal and subquery coalescing, describing the latter as similar in some ways to an inverse for “Or Expansion” and “Join Factorization”. In this instalment, it’s time to take a closer look at Or Expansion and we’ll move on to Join Factorization in the next instalment.

2022-11-30

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Question of the Day

ORDER BY alias

There is a table tmp_tab: 

CREATE TABLE tmp_tab (
id int,
val int
);
INSERT INTO tmp_tab VALUES
(1, 1),
(2, NULL),
(3, 3),
(4, 4),
(5, 5);
You want to order the rows ids by the following expression: 
    ISNULL(val, id) + 1
Which of the following queries produces the expected ordering and why? (Select all correct)

See possible answers