Обсуждение: Fwd: error in the example given for numeric data types

> Page: https://www.postgresql.org/docs/15/datatype-numeric.html

"docs/15" means this url pointer to pg version 15.

> practice=# create table t1(height numeric(3,5));
> ERROR:  NUMERIC scale 5 must be between 0 and precision 3
> LINE 1: create table t1(height numeric(3,5));
>  Please look into the matter and kindly revert back to me whatever you find
> out about this so that i can correct myself incase i misunderstood what the
> document says...

it works in pg15, not in pg14.
see my test: https://dbfiddle.uk/wgfjCx7j

jian he <jian.universality@gmail.com> writes:
>> practice=# create table t1(height numeric(3,5));
>> ERROR:  NUMERIC scale 5 must be between 0 and precision 3

> it works in pg15, not in pg14.
> see my test: https://dbfiddle.uk/wgfjCx7j

Indeed. The quoted documentation text is different between v15 and prior
versions.  Observe also the v15 release notes:

https://www.postgresql.org/docs/15/release-15.html

    E.4.3.4. Data Types

        Allow the scale of a numeric value to be negative, or greater than
        its precision (Dean Rasheed, Tom Lane)

        This allows rounding of values to the left of the decimal point,
        e.g., '1234'::numeric(4, -2) returns 1200.


            regards, tom lane

On 2023-07-15 12:08:26 +0530, Priyank Rajvansh wrote:
> Page: https://www.postgresql.org/docs/15/datatype-numeric.html
> Description:
>
> article 8.1.2 states the following:
>
> ''We use the following terms below: The precision of a numeric is the total
> count of significant digits in the whole number, that is, the number of
> digits to both sides of the decimal point. The scale of a numeric is the
> count of decimal digits in the fractional part, to the right of the decimal
> point. So the number 23.5141 has a precision of 6 and a scale of 4. Integers
> can be considered to have a scale of zero.''
>
> however it also states the following towards the end:
>
> '' For example, a column declared as
>
> NUMERIC(3, 5)
> will round values to 5 decimal places and can store values between -0.00999
> and 0.00999, inclusive.''
>
> Now from whatever i could decipher the syntax of the numeric data type is
> NUMERIC(precision,scale) and if we write NUMERIC (3,5) it would mean that we
> are trying to store a number which has 3 digits in total and 5 of them are
> to the right of the decimal point, which doesn't make sense !

It may sound weird but it does make sense. There are three digits in the
number and the rightmost of them is five positions to the right of the
decimal pointis. So you can store

    0.00999
    --12345

but not

    0.01000
    --12345

as that would need a fourth digit
and also not
    0.000123
    --123456
as not the rightmost digit is now six places right of the decimal
point.

Mathematically you store an integer with 3 digits and multiply it with
10^-5 to get the value.

        hp

--
   _  | Peter J. Holzer    | Story must make more sense than reality.
|_|_) |                    |
| |   | hjp@hjp.at         |    -- Charles Stross, "Creative writing
__/   | http://www.hjp.at/ |       challenge!"