Re: Explicit deterministic COLLATE fails with pattern matchingoperations on column with non-deterministic collation
| От | David G. Johnston |
|---|---|
| Тема | Re: Explicit deterministic COLLATE fails with pattern matchingoperations on column with non-deterministic collation |
| Дата | |
| Msg-id | CAKFQuwZakFfXX3m5K5oMg9WJgQT6FffLRjYQzJQgTH1pGOOz5Q@mail.gmail.com обсуждение исходный текст |
| Ответ на | Explicit deterministic COLLATE fails with pattern matching operationson column with non-deterministic collation (James Lucas <jlucasdba@gmail.com>) |
| Ответы |
Re: Explicit deterministic COLLATE fails with pattern matchingoperations on column with non-deterministic collation
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| Список | pgsql-bugs |
On Wed, May 27, 2020 at 8:23 AM James Lucas <jlucasdba@gmail.com> wrote:
create table ctestnd (id numeric, t text collate mycollation);
create index ctestnd_idx02 on ctestnd (t collate "C");
Test on ctestnd:
explain select * from ctestnd where t = 'aAa' collate "C";
QUERY PLAN
------------------------------------------------------------------------------
Index Scan using ctestnd_idx02 on ctestnd (cost=0.42..4.44 rows=1 width=10)
Index Cond: (t = 'aAa'::text COLLATE "C")
COMMENT: Works as expected.
Uses an index scan which is where the deterministic collation exists
explain select * from ctestnd where t like 'a%';
ERROR: nondeterministic collations are not supported for LIKE
COMMENT: Fails as expected.
explain select * from ctestnd where t like 'a%' collate "C";
ERROR: nondeterministic collations are not supported for LIKE
Your schema is inherently unstable in this respect because the planner has to be allowed to choose a sequential scan and as soon as it does it attempts to perform like comparisons with table data that is stored using a non-deterministic collation.
I don't know what kinds of promises we make about implicit collation manipulation here but absent such a transformation the sequential scan plan with LIKE generates an invalid plan choice. That it doesn't go find the index that happens to have a workable collation for the query is unsurprising - whether that is even a possibility is beyond me.
David J.
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