Re: Query with no result set, really really slow adding ORBDER BY / LIMIT clause

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2017-04-21 9:05 GMT+02:00 Marco Renzi <renzi.mrc@xxxxxxxxx>:


I am thinking so limit 10000 should be ok. Too big number can be messy for optimizer similarly like too small number.

The planner is driven by statistics - and the statistics are not perfect - usually it is working on 80% - like weather forecasting.

Usually it is working, but sometimes not.

Regards

Pavel
 


Thanks Pavel, i almost found two solutions at the end:
One is to use an inner limit as you said, and the other, when you just know what the filter is,
is to try to join with SELECTS that have to be executed first from the planner.

Eg
SELECT  fase.id
FROM            tipofase
JOIN       fase
ON         (fase.tipofase = (SELECT tipofase.id FROM tipofase WHERE tipofase.agendafrontoffice = true))

ORDER BY        fase.id DESC   limit 10 offset 0

Thanks for the help

yes, sometimes when the data are not homogeneous more queries are necessary

Regards

Pavel
 

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Ing. Marco Renzi
OCA - Oracle Certified Associate Java SE7 Programmer
OCP - Oracle Certified Mysql 5 Developer

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