How to display column name and column comment, when try DML - sql

Question

I'm try use DML operations on table, when insert or update. I need to show column name and column comment when the operation failed. For example code:
CREATE TABLE test_test(col1 VARCHAR2(10), col2 VARCHAR2(100) not null);
DECLARE
ex_insert_null EXCEPTION;
PRAGMA EXCEPTION_INIT(ex_insert_null, -1400);
ex_value_too_large EXCEPTION;
PRAGMA EXCEPTION_INIT(ex_value_too_large, -12899);
BEGIN
INSERT INTO test_test
(col1
,col2)
SELECT CASE
WHEN LEVEL = 8 THEN
(LEVEL + 1) || 'qqqqqqqqqqqq'
ELSE
(LEVEL + 2) || 'qqq'
END AS col1
,CASE
WHEN LEVEL = 7 THEN
NULL
ELSE
(LEVEL + 3) || 'wwwwwww'
END AS col2
FROM dual
CONNECT BY LEVEL <= 10;
COMMIT;
EXCEPTION
WHEN ex_insert_null THEN
ROLLBACK;
dbms_output.put_line('ex_insert_null at ' || ' ' /* || column_name || ' ' || column_comment */);
WHEN ex_value_too_large THEN
ROLLBACK;
dbms_output.put_line('ex_value_too_large at ' || ' ' /* || column_name || ' ' || column_comment */);
END;
/

Answer 1

As APC has pointed out, you could use "existing Oracle exceptions" eg if you had something like ...
procedure insert_( col1 varchar2, col2 varchar2 )
is
v_errorcode varchar2(64) ;
v_errormsg varchar2(128) ;
begin
insert into t ( c1, c2 ) values ( col1, col2 ) ;
exception
when others then
if sqlcode = -1400 or sqlcode = -12899 then
v_errorcode := sqlcode;
v_errormsg := substr( sqlerrm, 1, 128 );
dbms_output.put_line( v_errorcode || ' ' || v_errormsg ) ;
raise;
end if;
end insert_ ;
... you could get error messages such as these:
-1400 ORA-01400: cannot insert NULL into ("MYSCHEMA"."T"."C2")
-12899 ORA-12899: value too large for column "MYSCHEMA"."T"."C1" (actual: 13, maximum: 10)
If this is enough information for you, fine. However, you also want to see the COMMENTS for the columns. Although we could get the column names from the SQLERRM strings, it may be more reliable to use user-defined exceptions (as you have hinted).
As a starting point, the following DDL and PACKAGE code may be of use for you. ( see also: dbfiddle here )
Tables:
drop table t cascade constraints ;
drop table errorlog cascade constraints ;
create table t (
c1 varchar2(10)
, c2 varchar2(64) not null
) ;
comment on column t.c1 is 'this is the column comment for c1';
comment on column t.c2 is 'this is the column comment for c2';
create table errorlog (
when_ timestamp
, msg varchar2(4000)
) ;
Package spec
create or replace package P is
-- insert into T, throwing exceptions
procedure insert_( col1 varchar2, col2 varchar2 );
-- use your example SELECT, call the insert_ procedure
procedure insert_test ;
-- retrieve the column comments from user_col_comments
function fetch_comment( table_ varchar2, col_ varchar2 ) return varchar2 ;
end P ;
/
Package body
create or replace package body P is
procedure insert_( col1 varchar2, col2 varchar2 )
is
ex_value_too_large exception ; -- T.c1: varchar2(10)
ex_insert_null exception ; -- T.c2: cannot be null
v_errorcol varchar2(32) := '' ;
v_comment varchar2(128) := '' ;
v_tablename constant varchar2(32) := upper('T') ;
begin
if length( col1 ) > 10 then
v_errorcol := upper('C1') ;
raise ex_value_too_large ;
end if;
if col2 is null then
v_errorcol := upper('C2') ;
raise ex_insert_null ;
end if ;
insert into t ( c1, c2 ) values ( col1, col2 ) ;
exception
when ex_value_too_large then
dbms_output.put_line( ' ex_value_too_large # '
|| v_errorcol || ' (' || fetch_comment( v_tablename, v_errorcol ) || ')' );
when ex_insert_null then
dbms_output.put_line( ' ex_insert_null # '
|| v_errorcol || ' (' || fetch_comment( v_tablename, v_errorcol ) || ')' );
when others then
raise ;
end insert_ ;
procedure insert_test
is
begin
for rec_ in (
select
case
when level = 8 then ( level + 1 ) || 'qqqqqqqqqqqq'
else ( level + 2 ) || 'qqq'
end as col1
, case
when level = 7 then null
else ( level + 3 ) || 'wwwwwww'
end as col2
from dual
connect by level <= 10
) loop
insert_( rec_.col1, rec_.col2 ) ;
end loop;
commit;
end insert_test;
function fetch_comment( table_ varchar2, col_ varchar2 ) return varchar2
is
v_comment varchar2(4000) ; -- same datatype as in user_tab_comments
begin
select comments into v_comment
from user_col_comments
where table_name = table_
and column_name = col_ ;
return v_comment ;
end fetch_comment ;
end P ;
/
For testing the package code, execute the following anonymous block:
begin
P.insert_test ;
end;
/
-- output
ex_insert_null # C2 (this is the column comment for c2)
ex_value_too_large # C1 (this is the column comment for c1)
-- Table T contains:
SQL> select * from T;
C1 C2
3qqq 4wwwwwww
4qqq 5wwwwwww
5qqq 6wwwwwww
6qqq 7wwwwwww
7qqq 8wwwwwww
8qqq 9wwwwwww
11qqq 12wwwwwww
12qqq 13wwwwwww
In the dbfiddle, all output will be written to T and ERRORLOG, respectively. You can also use dbms_output.put_line (which is commented out in the dbfiddle) if needed. Notice that the cursor for loop in the insert_test procedure is inefficient (we could use BULK operations). Also, you need to decide where and how the exceptions are handled. As mentioned, this example is just a starting point - which will probably need lots of refinements.