On 2-2-2018 17:25, Alex Peshkoff via Firebird-devel wrote:
On 02/02/18 10:57, Dmitry Yemanov wrote:
I tend to agree that there's no sense to use yet another data type at
the API side. SQL_DEC16/DEC34 can be easily used instead.
I.e. to represent NUMERIC/DECIMAL(M, N) where M > 18 will be used
SQL_DEC34 with sqlsubtype 1/2? But what should be the value of
sql_scale? On the one hand in should be non-zero to let user know how
many digits after decimal point may be used. On the other - for non-zero
scale in numeric fields we always used to follow the rule: value =
basic-type-value * pow(10, -scale) but most of people here tend to
require SQL_DEC34 to be already scaled correctly.
Let's make final choice before making any changes.
I propose that the scale is communicated when requesting info on columns
or parameters using isc_info_sql_scale, but it should be removed from
the request blr as it is part of the Decimal128 value.
The fact that for p <= 18 decimal/numeric the sql_scale information is
used for the necessary rescaling is just an implementation detail. When
we communicate the scale inline in the Decimal128, it is still pertinent
metadata that needs to be communicated in some way (eg I need to know,
because that is a requirement of the JDBC specification). Not putting it
in sql_scale wouldn't make a lot of sense to me, because it is by
definition the expected/defined scale of the column or parameter, so it
is the right place to put that in.
Isn't it the case already (for SQL_DEC_FIXED)? sqlsubtype was always
used to indicate INTEGER vs NUMERIC vs DECIMAL, I suppose it's
preserved for SQL_DEC_FIXED and can be used for SQL_DEC16/DEC34 too.
sqlsubtype is always zero now but certainly this can be changed.
It will need to be changed if we want to be able discern numeric and
decimal (in the current form) or decfloat, numeric and decimal (in the
proposed form).
BTW - the difference between NUMERIC vs DECIMAL in firebird is lost.
According to standard DECIMAL(s,p) must be exactly as precise as
declared, while NUMERIC(s,p) must be at least as precise as declared. In
firebird both behave as NUMERIC.
It is exactly the reverse, Firebird DECIMAL is compliant with the spec,
NUMERIC isn't:
"""
26) NUMERIC specifies the data type exact numeric, with the decimal
precision and scale specified by the <precision> and <scale>.
27) DECIMAL specifies the data type exact numeric, with the decimal
scale specified by the <scale> and the implementation-defined decimal
precision equal to or greater than the value of the specified <precision>.
"""
We could consider 'deprecating' NUMERIC, and only apply the extended
precision to DECIMAL, but that might be more confusing.
Mark
--
Mark Rotteveel
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