Thread

1. Numeric Type Precision Not Respected in Function or Procedure Arguments

   Aaron Ackerman <aackerman@goodmorning.com> — 2025-09-22T19:39:38Z

   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;
   ```
   
   
   
   

2. Re: Numeric Type Precision Not Respected in Function or Procedure Arguments

   Tom Lane <tgl@sss.pgh.pa.us> — 2025-09-22T21:31:07Z

   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
   
   
   
   

3. Re: Numeric Type Precision Not Respected in Function or Procedure Arguments

   David G. Johnston <david.g.johnston@gmail.com> — 2025-09-22T21:33:45Z

   On Monday, September 22, 2025, Aaron Ackerman <aackerman@goodmorning.com>
   wrote:
   
   > 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).
   >
   
   This is a known limitation - the “typmod” (type modifier) is not stored in
   the metadata for a function’s interface.
   
   Pretty sure it’s documented but not able to go hunting for it at the moment.
   
   David J.