Allow numeric scale to be negative or greater than precision

Enterprise / PostgreSQL - Dean Rasheed [gmail.com] - 26 July 2021 13:13 UTC

Formerly, when specifying NUMERIC(precision, scale), the scale had to be in the range [0, precision], which was per SQL spec. This commit extends the range of allowed scales to [-1000, 1000], independent of the precision (whose valid range remains [1, 1000]).

A negative scale implies rounding before the decimal point. For example, a column might be declared with a scale of -3 to round values to the nearest thousand. Note that the display scale remains non-negative, so in this case the display scale will be zero, and all digits before the decimal point will be displayed.

A scale greater than the precision supports fractional values with zeros immediately after the decimal point.

Take the opportunity to tidy up the code that packs, unpacks and
validates the contents of a typmod integer, encapsulating it in a small set of new inline functions.

Bump the catversion because the allowed contents of atttypmod have changed for numeric columns. This isn't a change that requires a re-initdb, but negative scale values in the typmod would confuse old backends.

Dean Rasheed, with additional improvements by Tom Lane. Reviewed by Tom Lane.

Discussion: https://postgr.es/m/CAEZATCWdNLgpKihmURF8nfofP0RFtAKJ7ktY6GcZOPnMfUoRqA@mail.gmail.com

085f931f52 Allow numeric scale to be negative or greater than precision.
doc/src/sgml/datatype.sgml | 48 ++++++++++-
src/backend/utils/adt/numeric.c | 130 +++++++++++++++++++++--------
src/include/catalog/catversion.h | 2 +-
src/include/utils/numeric.h | 16 +++-
src/test/regress/expected/numeric.out | 63 ++++++++++++++
src/test/regress/expected/sanity_check.out | 1 +
src/test/regress/sql/numeric.sql | 34 ++++++++
7 files changed, 251 insertions(+), 43 deletions(-)

Upstream: git.postgresql.org


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