sql: fix casts between REG* types #75112
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The newly introduced `castMap` does not contain entries for casts between all combinations of REG* types, which is consistent with Postgres, but inconsistent with behavior in versions up to 21.2 where these casts are allowed. The `castMap` changes result in more than just backward incompatibility. We allow branches of CASE statements to be equivalent types (i.e., types in the same family), like `REGCLASS` and `REGTYPE`, and we automatically add casts to a query plan to support this. However, because these casts don't exist in the `castMap`, internal errors are raised when we try to fetch the volatility of the cast while building logical properties. According to Postgres's type conversion rules for CASE, we should only allow branches to be different types if they can be implicitly cast to the first non-NULL branch. Implicit casts between REG* types are not allowed, so CASE expressions with branches of different REG* types should result in a user error like `CASE/WHEN could not convert type regclass to regtype`. However, this is a much larger project and the change will not be fully backward compatible. This work is tracked by issue cockroachdb#75103. For now, this commit adds casts between REG* types to the `castMap` to maintain backward compatibility and prevent an internal error. There is no release note because this bug does not exist in any releases. Fixes cockroachdb#74784 Release note: None
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The newly introduced
castMapdoes not contain entries for castsbetween all combinations of REG* types, which is consistent with
Postgres, but inconsistent with behavior in versions up to 21.2 where
these casts are allowed.
The
castMapchanges result in more than just backward incompatibility.We allow branches of CASE statements to be equivalent types (i.e., types
in the same family), like
REGCLASSandREGTYPE, and we automaticallyadd casts to a query plan to support this. However, because these casts
don't exist in the
castMap, internal errors are raised when we try tofetch the volatility of the cast while building logical properties.
According to Postgres's type conversion rules for CASE, we should only
allow branches to be different types if they can be implicitly cast to
the first non-NULL branch. Implicit casts between REG* types are not
allowed, so CASE expressions with branches of different REG* types
should result in a user error like
CASE/WHEN could not convert type regclass to regtype. However, this is a much larger project and thechange will not be fully backward compatible. This work is tracked by
issue #75103.
For now, this commit adds casts between REG* types to the
castMaptomaintain backward compatibility and prevent an internal error.
There is no release note because this bug does not exist in any
releases.
Fixes #74784
Release note: None