Column name in error text: value too long for type character - postgresql

Question

We have a table with 2 columns (both have the same type and size) and 2 constraints for them:
create table colors
(
color varchar(6)
constraint color_check check
((color)::text ~ '^[0-9a-fA-F]{6}$'::text),
color_secodandry varchar(6)
constraint color_secondary_check check
((color_secodandry)::text ~ '^[0-9a-fA-F]{6}$'::text),
);
In case of inserts with long values:
insert into colors (color, color_secondary) values ('ccaabb', 'TOO_LONG_TEXT');
insert into colors (color, color_secondary) values ('TOO_LONG_TEXT', 'ccaabb');
we'll get the same errors for two error cases:
ERROR: value too long for type character varying(6) (SQLSTATE 22001)
PostgreSQL validates length for that columns before make inserts, so our checks never run. Is there a way to understand, which column has an invalid data?

Answer 1

The issue you are having is the order of evaluation for the intended values. You told Postgres to not allow a length over 6 (character varying(6)) you also specified additional certain criteria those values have to satisfy. What is happening is Postgres validates the length criteria and throws an exception when the value fails, in that case the check constraint is not preformed as Postgres works on an exit on first failure. The check constraint is processed only after the length passes. Example:
create table test1( id integer generated always as identity
, color6 character varying (6)
constraint color6_check check (color6 ~ '^[0-9a-fA-F]{6}$')
, color60 character varying (60)
constraint color60_check check (color60 ~ '^[0-9a-fA-F]{6}$')
) ;
insert into test1( color6 ) values ('aabbccdd') ;
/* Result
SQL Error [22001]: ERROR: value too long for type character varying(6)
ERROR: value too long for type character varying(6)
*/
insert into test1( color60 ) values ('aabbccdd') ;
/* Result
SQL Error [23514]: ERROR: new row for relation "test1" violates check constraint "color60_check"
Detail: Failing row contains (3, null, aabbccdd).
ERROR: new row for relation "test1" violates check constraint "color60_check"
*/
Notice the only difference between them is the length specification for the column being inserted. Yet they fail, but for a different reasons. Since both the length specification and the check constraint enforce the length you need to decide now how you want to handle the 2 conditions: a separate error for each condition or a single error for both. (IMHO: separate messages)