queries with subquery constraints on partitioned tables not optimized?

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 Let's say you have one partitioned table, "tbl_p", partitioned according to 
the PK "p_pk". I have made something similar with triggers, basing myself on 
the manual for making partitioned tables.
According to the manual, optimizer searches the CHECKs of the partitions to 
determine which table(s) to use (if applicable).

So if one has CHECKs of kind "p_pk = some number", queries like "SELECT * 
from tbl_p where p_pk = 1" will only be searched in the appropriate table. 
One can check this with EXPLAIN. So far so good.

Now, if one takes a subquery for "1", the optimizer evaluates it first 
(let's say to "1"), but then searches for it (sequentially) in every 
partition, which, for large partitions, can be very time-consuming and goes 
beyond the point of partitioning.

Is this normal, or am I missing something?

Kind regards,
Davor




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