Обсуждение: Numeric Type Precision Not Respected in Function or Procedure Arguments

When a NUMERIC type is used as a function or procedure argument, the
value does not actually follow the user-defined precision, such as
NUMERIC(10,4). It does not round off the value to the specified scale
or check for an overflow error. Return type of function also does not
respect precision. This does not apply to the declared variables,
which have the expected behaviour. Tables, custom types, and explicit
casting also all have the expected behaviour for me, rounding the
value off and checking for overflow.

Version: PostgreSQL 16.2 (Ubuntu 16.2-1.pgdg22.04+1) on
x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 11.4.0-1ubuntu1~22.04)
11.4.0, 64-bit

```
CREATE OR REPLACE FUNCTION numericsTestingFunction(
    input NUMERIC(4,3))
RETURNS NUMERIC(4,3)
LANGUAGE plpgsql STABLE
AS $$
BEGIN
    RETURN input;
END; $$;

-- Returns 98765.123456789, but expected error
SELECT * FROM numericsTestingFunction(98765.123456789);

-- Returns 5.123456789, but expected 5.123
SELECT * FROM numericsTestingFunction(5.123456789);

CREATE OR REPLACE PROCEDURE numericsTestingProcedure(
    input NUMERIC(4,3))
LANGUAGE plpgsql
AS $$
DECLARE declared NUMERIC(4,3);
BEGIN
    SELECT input INTO declared;
    RAISE NOTICE 'Input value: %, Into declared: %', input, declared;
END; $$;

-- Raises:   'Input value: 5.123456789, Into declared: 5.123'
-- Expected: 'Input value: 5.1234, Into declared: 5.123'
CALL numericsTestingProcedure(5.123456789);

DROP FUNCTION numericsTestingFunction;
DROP PROCEDURE numericsTestingProcedure;
```

Aaron Ackerman <aackerman@goodmorning.com> writes:
> When a NUMERIC type is used as a function or procedure argument, the
> value does not actually follow the user-defined precision, such as
> NUMERIC(10,4). It does not round off the value to the specified scale
> or check for an overflow error. Return type of function also does not
> respect precision.

This is documented.  See for example in [1]:

    The full SQL type syntax is allowed for declaring a function's
    arguments and return value. However, parenthesized type modifiers
    (e.g., the precision field for type numeric) are discarded by
    CREATE FUNCTION. Thus for example CREATE FUNCTION foo
    (varchar(10)) ... is exactly the same as CREATE FUNCTION foo
    (varchar) ....

Perhaps we should reject type modifiers in CREATE FUNCTION,
since people do get confused about this.  (The alternative of
actually doing something with them is in aint-gonna-happen
territory, I think.)

            regards, tom lane

[1] https://www.postgresql.org/docs/current/sql-createfunction.html

When a NUMERIC type is used as a function or procedure argument, the
value does not actually follow the user-defined precision, such as
NUMERIC(10,4).