PL/SQL value_error exception not getting caught - oracle

Question

This is my Department table:
create table Department(
DeptNo int primary key,
DeptName varchar2(21) not null,
DeptLocation varchar2(13) not null
);
I am trying to insert value for DeptName column with length more than accepted i.e. 21, which means I should get "VALUE_ERROR" exception.
The plsql code I am running is:
begin
insert into department values(1, 'Some random department name', 'SomeLocation');
exception
when value_error then
dbms_output.put_line('Cannot store the value!');
end;
As I am trying to catch the exception, it is not getting caught. I am getting the error:
ORA-12899: value too large for column "SQL_ZIRHWMLFPCEAKPGYGJJZLSIFI"."DEPARTMENT"."DEPTNAME" (actual: 27, maximum: 21) ORA-06512: at line 2
ORA-06512: at "SYS.DBMS_SQL", line 1721
But if I change my exception from "value_error" to "others"
begin
insert into department values(1, 'Some random department name', 'SomeLocation');
exception
when others then
dbms_output.put_line('Cannot store the value!');
end;
then I get the expected output
Cannot store the value!
Where could I have gone wrong? Please let me know. Thanks!
PS: I am running all the code on livesql.oracle.com

Answer 1

Ideally, what you are using is correct and it should had worked as desired. But the exception VALUE_ERROR behaves differently in somecases. See the below illustrative example.
As per the documentation value_error comes when there is an
arithmetic, conversion, truncation, or size-constraint error occurs.
For example, when your program selects a column value into a character
variable, if the value is longer than the declared length of the
variable, PL/SQL aborts the assignment and raises VALUE_ERROR. In
procedural statements, VALUE_ERROR is raised if the conversion of a
character string into a number fails.
The last line says, In procedural statements, VALUE_ERROR is raised if the conversion of a character string into a number fails., but when i run this in a block it rasied INVALID_NUMBER exception.
SQL> declare
2 n number;
3 begin
4 select to_number('a')
5 into n
6 from dual
7 ;
8 exception
9 when value_error
10 then
11 dbms_output.put_line ('Value Error');
12 when invalid_number
13 then
14 dbms_output.put_line ('Invalid Number');
15 end;
16 /
Invalid Number
PL/SQL procedure successfully completed.
I expected that it would raise the VALUE_ERROR but it didn't. So it might be the case that Oracle was not able to raise value_error in your case and when you used WHEN OTHERS it was caught.
Edit:
Ok. So is it possible somehow to catch value_error exception by giving
the value longer than the declared length of the variable?
Explicit Raise of System Exception : Not very elegant but you can do it as below.
declare
var int;
var1 varchar2(21);
var2 varchar2(13);
begin
var1:='Some random department name';
var2:= 'SomeLocation'
If var1 > 21 then
RAISE VALUE_ERROR;
END IF;
If var2 > 13 then
RAISE VALUE_ERROR;
END IF;
insert into department values(1, var1, var2);
exception
when value_error then
dbms_output.put_line('Cannot store the value!');
end;

Answer 2

VALUE_ERROR was not the exception raised when you ran your code, if you want, you can defined an EXCEPTION and catch it, see below code for sample,
DECLARE
ORA_12899 EXCEPTION;
PRAGMA EXCEPTION_INIT(ORA_12899, -12899);
begin
insert into department values(1, 'Some random department name', 'SomeLocation');
exception
when ORA_12899 then
dbms_output.put_line('Cannot store the value!');
end;
/
Below code will have a VALUE_ERROR;
DECLARE
ORA_12899 EXCEPTION;
PRAGMA EXCEPTION_INIT(ORA_12899, -12899);
v_dept VARCHAR2(20);
begin
v_dept := 'Some random department name';
insert into department values(1, v_dept, 'SomeLocation');
exception
when ORA_12899 then
dbms_output.put_line('Cannot store the value!');
end;
/