Обсуждение: BUG #17166: PREPARE without types inconsistent type resolving
The following bug has been logged on the website: Bug reference: 17166 Logged by: Daniel Sonck Email address: daniel@sonck.nl PostgreSQL version: 13.3 Operating system: Linux (Archlinux) Description: When executing the following statement, the type of $1 could not be deduced: SELECT * FROM my_table WHERE ($1 IS NULL OR col = $1); However, when executing the following statement, the type of $1 could be deduced: SELECT * FROM my_table WHERE (col = $1 OR $1 IS NULL); While both queries end result are the same, the first is more in line with the meaning, saying that the optional parameter $1 may be NULL, or, if it's not, results should be filtered by col = $1. It is rather curious that a simple order affects the type of $1. I would imagine that, as $1 IS NULL has no type implications, the col = $1 would determine the type of $1.
On Sunday, August 29, 2021, PG Bug reporting form <noreply@postgresql.org> wrote:
It is rather curious that a
simple order affects the type of $1. I would imagine that, as $1 IS NULL has
no type implications, the col = $1 would determine the type of $1.
The system resolves the type of each argument at its first encounter while parsing. It has to make a choice, and since “is null” doesn’t provide any help, it is unable to make a decision. Null “values” are still typed.
This is documented under the PREPARE SQL command reference (the only pure sql way to use numbered parameters) and so is definitely not a bug.
David J.