Re: Sanity Check - Correlated Select Subquery SQL rewrite equivalent? Or no?

From: Chris Taylor <christopherdtaylor1994_at_gmail.com>
Date: Thu, 2 Feb 2023 09:13:59 -0500
Message-ID: <CAP79kiTC1ZKFddK9=M-9YSc7Cgajy2HUNaGxkLiQ7g5vqYnkPA_at_mail.gmail.com>

_at_Dominic / _at_Sayan

So my SQL skills have a strong weakness when it comes to understanding when/how to use EXISTS (NOT EXISTS) regularly. Can you help me understand by explaining how this rewrite is equivalent when the first query uses a MAX function?

(I hate that I have to ask but I'm having a hard time understanding how this works out)

My lead developer mentions this:
*"If I’m not mistaken this is a table where for every single new flight plan (even if for the same leg) we have a new row, and the select seeks to get the latest.*

*Both of your versions do not cater for the latest version, right?"*

What's killing me is that the MAX() function in the original is referencing the outer table which breaks my brain.
(I'm trying to work through it myself as well to understand)

Original

Rewritten

SELECT FPE.COL1, FPE.COL2, FPE.COL3, FPE.ID
<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C0b18ac90f2044325546f08db046a9261%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108628037188702%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=cWQlSnsYk3NZCzd3Ab3Mq9ibclbXkAcHfL0OT85d6Io%3D&reserved=0>
,

FPE.COL4, FPE.VERSION FROM F_PLAN FPE WHERE (FPE.ID
<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C0b18ac90f2044325546f08db046a9261%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108628037188702%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=cWQlSnsYk3NZCzd3Ab3Mq9ibclbXkAcHfL0OT85d6Io%3D&reserved=0>
IN

(SELECT MAX (FPE.ID
<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C0b18ac90f2044325546f08db046a9261%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108628037188702%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=cWQlSnsYk3NZCzd3Ab3Mq9ibclbXkAcHfL0OT85d6Io%3D&reserved=0>
)

                 FROM F_PLAN

                WHERE FPE.COL3 IN

                          ('some_guid_id_1',

                           'some_guid_id_2')

              )

          )

ORDER BY FPE.ID
<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C0b18ac90f2044325546f08db046a9261%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108628037188702%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=cWQlSnsYk3NZCzd3Ab3Mq9ibclbXkAcHfL0OT85d6Io%3D&reserved=0>

SELECT FPE.COL1,
       FPE.COL2,
       FPE.COL3,
       FPE.ID

<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>
,

       FPE.COL4,
       FPE.VERSION

FROM F_PLAN FPE
WHERE FPE.ID
<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>
is
not null
and exists (SELECT 0 FROM F_PLAN)
and FPE.COL3 IN ('some_guid_id_1','some_guid_id_2') ORDER BY FPE.ID
<https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>

Thanks,

Chris

On Wed, Feb 1, 2023 at 12:00 PM Dominic Brooks <dombrooks_at_hotmail.com> wrote:

> Oh good spot – the FPE. Alias within MAX(FPE.ID) seems so obvious now....
> how did I miss it 😊
>
>
>
>
>
> *From: *Sayan Malakshinov <xt.and.r_at_gmail.com>
> *Sent: *01 February 2023 16:57
> *To: *gogala.mladen_at_gmail.com
> *Cc: *oracle-l_at_freelists.org
> *Subject: *Re: Sanity Check - Correlated Select Subquery SQL rewrite
> equivalent? Or no?
>
>
>
> Since that subquery has no any columns from F_PLAN nor predicates by
> columns from F_PLAN, we can rewrite original
>
>   SELECT FPE.COL1,
>          FPE.COL2,
>          FPE.COL3,
>          FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605540044%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=65mR53YTMHUZdLJhWpm%2FNsMkXaFC5%2BRm8v3S5Xn%2FTJw%3D&reserved=0>
> ,
>          FPE.COL4,
>          FPE.VERSION
>     FROM F_PLAN FPE
>    WHERE (FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605540044%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=65mR53YTMHUZdLJhWpm%2FNsMkXaFC5%2BRm8v3S5Xn%2FTJw%3D&reserved=0>
> IN
>               (SELECT MAX (*FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605540044%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=65mR53YTMHUZdLJhWpm%2FNsMkXaFC5%2BRm8v3S5Xn%2FTJw%3D&reserved=0>*
> )
>                  FROM F_PLAN
>                 WHERE* FPE.COL3* IN
>                           ('some_guid_id_1',
>                            'some_guid_id_2')))
> ORDER BY FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>
>
>
>
> as
>
>
>
> SELECT FPE.COL1,
>        FPE.COL2,
>        FPE.COL3,
>        FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>
> ,
>        FPE.COL4,
>        FPE.VERSION
> FROM F_PLAN FPE
> WHERE FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>
> is not null
>  and exists (SELECT 0 FROM F_PLAN)
>  and FPE.COL3 IN ('some_guid_id_1','some_guid_id_2')
> ORDER BY FPE.ID
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ffpe.id%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v4j5UFcyATdPbEaoauNsvCRbq3ARLaoRQSfAob4XXPY%3D&reserved=0>
>
>
>
> On Wed, Feb 1, 2023 at 4:42 PM Mladen Gogala <gogala.mladen_at_gmail.com>
> wrote:
>
> On 2/1/23 11:19, Clay Jackson (Clay.Jackson) wrote:
>
> What Dominic said –
>
>
>
> Among other things –
>
>
>
> where FPE.COL3 = T1.COL3
>
>
>
> is NOT part of the predicate in the original query
>
>
>
> Not only that, the 2nd query doesn't have MAX function in it, thereby
> being definitely not equivalent. I would probably try to separate the
> subquery into a WITH clause, materialize and do join.
>
> Regards
>
> --
>
> Mladen Gogala
>
> Database Consultant
>
> Tel: (347) 321-1217
>
> https://dbwhisperer.wordpress.com <https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdbwhisperer.wordpress.com%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=KRb7WaFr9WygzFaKIlO2adcfe2pXNgJQ3VzpVMl4Z7U%3D&reserved=0>
>
>
>
>
> --
>
> Best regards,
> Sayan Malakshinov
>
> Oracle performance tuning engineer
>
> Oracle ACE
> http://orasql.org
> <https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Forasql.org%2F&data=05%7C01%7C%7C40c1698e781f4d5ae91108db047569b1%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638108674605696751%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=%2FkgXwMfPbJtaD6tkKVyxrEtyoIeLiCv75AfguRa1W5Q%3D&reserved=0>
>
>
>

--
http://www.freelists.org/webpage/oracle-l

Received on Thu Feb 02 2023 - 15:13:59 CET

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