Can I see the DML inside an Oracle trigger? - oracle

Question

Is it possible to see the DML (SQL Statement) that is being run that caused a trigger to be executed?
For example, inside an INSERT trigger I would like to get this:
"insert into myTable (name) values ('Fred')"
I read about ora_sql_txt(sql_text) in articles such as this but couldn't get it working - not sure if that is even leading me down the right path?
We are using Oracle 10.
Thank you in advance.
=========================
[EDITED] MORE DETAIL: We have the need to replicate an existing database (DB1) into a classified database (DB2) that is not accessible via the network. I need to keep these databases in sync. This is a one-way sync from (DB1) to (DB2), since (DB2) will contain additional tables and data that is not contained in the (DB1) system.
I have to determine a way to sync these databases without bringing them down (say, for a backup and restore) because it needs to stay live. So I thought that if I can store the actual DML being run (when data changes), I could "play-back" the DML on the new database to update it, just like someone was hand-entering it back in.
I can't bring over all the data because of the sheer size of it, and I can't just copy over the changed records because of FK constraints and the order in which I insert/update records. I figured that if I could "play-back" a log of what happened, using the exact SQL that changed the master, I could keep the databases in sync.
My current plan of attack was to keep a log of all records that were changed, inserted, and deleted and when I want to sync, the system generates DML to insert/update/delete those records. Then I just take the .SQL file to the classified system and run the script. The problem I'm running into are FKs. (Because when I generate the DML I only know what the current state of the data is, not it's path to get there - so ordering of statements is an issue). I guess I could disable all FK's, do the merge, then re-enable all FK's...
So - does my approach of storing the actual DML as-it-happens suck pondwater, or is there a better solution???

Answer 1

"does my approach of storing the actual DML as-it-happens suck pondwater?" Yes..
Strict ordering of the DML on your DB1 does not really exist. Multiple processes, muiltiple cores, things essentially happening at the essentially the same time.
And the DML, even when it happens sequentially doesn't act like it. Say the following two update statements run in seperate processes with seperate transactions, where the update in transaction 2 starts before transaction 1 commits:
update table_a set col_a = 10 where col_b = 'A' -- transaction 1
update table_a set col_c = 'Error' where col_a = 10 -- transaction 2
Since the changes made in the first transaction are not visibible to the second transaction, the rows changed by the second transaction will not include those of the first. But if you manage to capture the DML and replay it sequentially, transaction 1's changes will be visible, so transaction 2's changes will be different. (See pages 40 and 41 of Tom Kyte's Expert Oracle Database Architecture Second Edition.)
Hopefully you are using bind variables, so the DML by itself wouldn't be meaningful: update table_a set col_a = :col_a where id = :id Now what? Ok, so you want the DML with it's variable bindings.
Do you use sequences? If so, the next_val will not stay in synch between DB1 and DB2. (For example, instance failures can cause lost values, are both systems going to fail at the same time?) And if you are dealing with RAC, where the next_val varies depending on node, forget it.
I would start by investigating Oracle's replication.

Answer 2

I had a situation where I needed to move metadata/configuration changes (stored in a handful of tables) from a development environment to a production environment once tested. Something like Goldengate is the product to use for this but this can be costly and complicated to set up and administer.
The following procedure generates a trigger and attaches it to a table that needs the DML saved. The trigger re-creates the DML and in the following case saves it to an audit table - its up to you what you do with it. You can use the statements saved to the audit table to replay changes from a given point in time (cut and paste or develop a procedure to apply them to the target).
Hope you find this useful.
procedure gen_trigger( p_tname in varchar2 )
is
l_theCursor integer default dbms_sql.open_cursor;
l_query varchar2(1000) default 'select * from ' || p_tname;
l_colCnt number := 0;
l_descTbl dbms_sql.desc_tab;
trg varchar(32767) := null;
expr varchar(32767) := null;
cmd varchar(32767) := null;
begin
dbms_sql.parse( l_theCursor, l_query, dbms_sql.native );
dbms_sql.describe_columns( l_theCursor, l_colCnt, l_descTbl );
trg := q'#
create or replace trigger <%TABLE_NAME%>_audit
after insert or update or delete on <%TABLE_NAME%> for each row
declare
qs varchar2(20) := q'[q'^]';
qe varchar2(20) := q'[^']';
command clob;
nlsd varchar2(100);
begin
select value into nlsd from nls_session_parameters where parameter = 'NLS_DATE_FORMAT';
execute immediate 'alter session set nls_date_format = ''YYYY/MM/DD hh24:mi:ss'' ';
if inserting then
command := <%INSERT_COMMAND%>;
end if;
if updating then
command := <%UPDATE_COMMAND%>;
end if;
if deleting then
command := <%DELETE_COMMAND%>;
end if;
insert into x_audit values (systimestamp, command);
execute immediate q'+alter session set nls_date_format = '+'|| nlsd || q'+'+';
end;
#';
-- Create the insert command
cmd := q'#'insert into <%TABLE_NAME%> (<%INSERT_COLS%>) values ('||<%INSERT_VAL%>||')'#';
-- columns clause
for i in 1 .. l_colCnt loop
if expr is not null then
expr := expr || ',';
end if;
expr := expr || l_descTbl(i).col_name;
end loop;
cmd := replace(cmd,'<%INSERT_COLS%>',expr);
-- values clause
expr := null;
for i in 1 .. l_colCnt loop
if expr is not null then
expr := expr || q'#||','||#';
end if;
expr := expr || 'qs||:new.' || l_descTbl(i).col_name || '||qe';
end loop;
cmd := replace(cmd,'<%INSERT_VAL%>',expr);
trg := replace(trg,'<%INSERT_COMMAND%>',cmd);
-- create the update command
-- set clause
expr := null;
cmd := q'#'update <%TABLE_NAME%> set '||<%UPDATE_COLS%>||' where '||<%WHERE_CLAUSE%>#';
for i in 1 .. l_colCnt loop
if expr is not null then
expr := expr || q'#||','||#';
end if;
expr := expr || q'#'#' || l_descTbl(i).col_name || q'# = '||#'|| 'qs||:new.'||l_descTbl(i).col_name || '||qe';
end loop;
null;
cmd := replace(cmd,'<%UPDATE_COLS%>',expr);
trg := replace(trg,'<%UPDATE_COMMAND%>',cmd);
-- create the delete command
expr := null;
cmd := q'#'delete <%TABLE_NAME%> where '||<%WHERE_CLAUSE%>#';
trg := replace(trg,'<%DELETE_COMMAND%>',cmd);
-- where clause using primary key columns (used by update and delete)
expr := null;
for pk in (SELECT column_name FROM all_cons_columns WHERE constraint_name = (
SELECT constraint_name FROM user_constraints
WHERE UPPER(table_name) = UPPER(p_tname) AND CONSTRAINT_TYPE = 'P'
)) loop
if expr is not null then
expr := expr || q'#|| ' and '||#';
end if;
expr := expr || q'#'#' || pk.column_name || q'# = '||#'|| 'qs||:old.'|| pk.column_name || '||qe';
end loop;
if expr is null then -- must have a primary key
raise_application_error(-20000,'The table must have a primary key defined');
end if;
trg := replace(trg,'<%WHERE_CLAUSE%>',expr);
trg := replace(trg,'<%TABLE_NAME%>',p_tname);
execute immediate trg;
null;
exception
when others then
execute immediate 'alter session set nls_date_format=''YYYY/MM/DD'' ';
raise;
end;
/* Example
create table t1 (
col1 varchar2(100),
col2 number,
col3 date,
constraint pk_t1 primary key (col1)
)
/
BEGIN
GEN_TRIGGER('T1');
END;
/
-- Trigger generated ....
create or replace trigger t1_audit after
insert or
update or
delete on t1 for each row
declare
qs varchar2(20) := q'[q'^]';
qe varchar2(20) := q'[^']';
command clob;
nlsd varchar2(100);
begin
select value into nlsd from nls_session_parameters where parameter = 'NLS_DATE_FORMAT';
execute immediate 'alter session set nls_date_format = ''YYYY/MM/DD hh24:mi:ss'' ';
if inserting then
command := 'insert into T1 (COL1,COL2,COL3) values ('||qs||:new.col1||qe||','||qs||:new.col2||qe||','||qs||:new.col3||qe||')';
end if;
if updating then
command := 'update T1 set '||'COL1 = '||qs||:new.col1||qe||','||'COL2 = '||qs||:new.col2||qe||','||'COL3 = '||qs||:new.col3||qe||' where '||'COL1 = '||qs||:old.col1||qe;
end if;
if deleting then
command := 'delete T1 where '||'COL1 = '||qs||:old.col1||qe;
end if;
insert into x_audit values
(systimestamp, command
);
execute immediate q'+alter session set nls_date_format = '+'|| nlsd || q'+'+';
end;
*/

Answer 3

That function only works for 'event' triggers as discussed here.
You should look into Fine-Grained Auditing as a mechanism for this. Details here

Answer 4

When the trigger code runs don't you already know the dml that caused it to run?
CREATE OR REPLACE TRIGGER Print_salary_changes
BEFORE INSERT OR UPDATE ON Emp_tab
FOR EACH ROW
...
In this case it must have been an insert or an update statement on the emp_tab table.
To find out if it was an update or an insert
if inserting then
...
elsif updating then
...
end if;
The exact column values are available in the :old and :new pseudo-columns.