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Message-ID: <016e33b7-2830-4300-bc89-e7ce9e613bad@tantorlabs.com>
Date: Mon, 19 Aug 2024 12:38:05 +0300
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To: pgsql-hackers <pgsql-hackers@postgresql.org>
From: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Subject: Remove redundant NULL check in clause_selectivity_ext() function
Archived-At: <https://www.postgresql.org/message-id/016e33b7-2830-4300-bc89-e7ce9e613bad%40tantorlabs.com>
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Hi everyone,


In the `clause_selectivity_ext()` function, there’s a comment regarding 
a NULL clause check that asks, "can this still happen?". I decided to 
investigate whether this scenario is still valid.

Here’s what I found after reviewing the relevant cases:

- approx_tuple_count(): The function iterates over a loop of other clauses.
- get_foreign_key_join_selectivity(): The function is invoked within an 
`if (clause)` condition.
- consider_new_or_clause(): The clause is generated by 
`make_restrictinfo()`, which never returns NULL.
- clauselist_selectivity_ext(): This function either checks 
`list_length(clauses) == 1` before being called, or it is called within 
a loop of clauses.

In other cases, the function is called recursively from 
`clause_selectivity_ext()`.

If you are aware of any situations where a NULL clause could be passed 
or if I’ve missed anything, please let me know. I’m also open to any 
other suggestions.

-- 
Regards,
Ilia Evdokimov,
Tantor Labs LCC.

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