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From: Frédéric Yhuel <[email protected]>
To: Andrei Lepikhov <[email protected]>
To: Tom Lane <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Jehan-Guillaume de Rorthais <[email protected]>
Cc: Christophe Courtois <[email protected]>
Cc: Laurenz Albe <[email protected]>
Subject: Re: Indexes on expressions with multiple columns and operators
Date: Tue, 23 Sep 2025 12:20:44 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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On 9/22/25 23:15, Andrei Lepikhov wrote:
> I'm not sure I fully understand your case, but SQL Server demonstrates 
> an interesting approach: they have a WHERE clause attached to 
> statistics. So, having implemented this, you may separate the whole 
> range of values inside the table into 'partitions' by such a WHERE 
> condition.

Yes, from what I understood of the documentation [1], this is exactly 
what I would like!

> It may solve at least one issue with the 'dependencies' statistics: a 
> single number describing the dependency between any two values in the 
> columns often leads to incorrect estimations, as I see.

For what it's worth, I've never encountered a case in my life as a 
PostgreSQL support engineer where the 'dependency' kind could be useful. 
I only successfully used the 'mcv' kind once (and that was only 
partially successful, as it fixed the estimates but not the plan).

[1] 
https://learn.microsoft.com/en-us/sql/t-sql/statements/create-statistics-transact-sql?view=sql-serve...

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