Getting alternatives which contain SUBSTR(UID, 1, 0) when generating alternatives with Auto Optimize (4334090)

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Titolo

Getting alternatives which contain SUBSTR(UID, 1, 0) when generating alternatives with Auto Optimize
Descrizione

When using the SQL Rewrite | Auto Optimize option, there are always some alternative queries which contain
SUBSTR(UID, 1, 0).

For example and alternative to

select *
from emp
where emp.ename = 'AA'

is

select *
from emp
where emp.ename = 'AA' || SUBSTR(UID, 1, 0)

Why is this select better? It is really a better alternative?
Risoluzione

The objective is to give as many alternatives as possible for a select.
By concatenating SUBSTR(UID, 1, 0) to a char we do not add any value but we can change the oracle cost.
This can be helpful in some scenarios.
SUBSTR(UID, 1, 0) is used, as an example, any other Oracle function could have been used .
An empty string used to be concatenated, before ('AA'||''), but it doesn't work any more so the empty string was replaced by SUBSTR(UID, 1, 0) as it is runtime generated.

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Cronologia articoli:: Data di creazione: 8/29/2014
Ultimo aggiornamento: 5/7/2023

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