On 10-08-2020 17:17, Vlad Khorsun wrote:
Same function returning different types depending on input argument -
very bad idea,
I think. If we have some in the past it doesn't means we should add more
mess "just
because we can".
Except it isn't really an input argument. It is a keyword that defines
the behaviour (and the type) of the function. This is similar to for
example EXTRACT:
- EXTRACT(MILLISECOND FROM sometimestamp) returning NUMERIC(9,1)
- EXTRACT(SECOND FROM sometimestamp) returning NUMERIC(9,4)
- EXTRACT(WEEK FROM sometimestamp) returning SMALLINT (same goes for
most (all?) other types)
Is it possible to pass hash method as parameter ? If not now - could
it be possible
in the feature ? If yes - what type of result HASH should return for
CRC32 in this case
(i.e. when method name is passed as parameter) ?
The current behaviour would already 'break' in this situation, because
the length of the return value already depends on the type passed. So if
we are going to allow parameterization with an expression, that is
already a problem.
In any case that could be tackled because HASH(<expression> USING
<expression>) is a different function than HASH(<expression> USING
<keyword-hash-names>) and thus can have different return type (eg
VARBINARY that is long enough for all hashes), then HASH(<expression>
USING 'CRC32') would return say a VARBINARY(64) with 4 bytes, while
HASH(<expression> USING CRC32) returns an INTEGER.
Ideal, no, but pretty reasonable IMHO. Assuming we would even want such
functionality.
Currently, HASH supports MD5, SHA1, SHA256 and SHA512 - all these
algorithms are used
in cryptography, as Mark said in start message of this thread. Why mix
CRC32 in here ?
It is completely different alg for different purposes. What problem we
want to address
here ? BTW, any plans to add CRC64 ?
Nothing in the name of HASH suggests that all hashes applied must be
cryptographic. Currently HASH also supports PJW (as in HASH(value))
which is non-cryptograhic. We could even make this explicit by adding
HASH(value USING PJW) as an alias for HASH(value).
Mark
--
Mark Rotteveel
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