what does this mean "order by NULL"

Question

i use oracle 11g.what does the line order by null means in the following

select f_value,row_number() over (order by null) as id 
from tableName"

Answer 1

The OVER() clause for ROW_NUMBER() requires an ORDER BY

using ORDER BY NULL is a workaround that satifies the syntax requirement but does not actually change the order of the data. In effect it is an instruction to not order at all.

N.B.: some (myself included) prefer to use SELECT 1 instead of SELECT NULL but there is no difference in effect.

Bottom line: not great, but it works.

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tip: TSQL does not permit the direct use of SELECT 1, but you may use (SELECT 1)