plsql Trigger to generate and insert values - sql

Question

I am trying to create a trigger to automatic generate and insert values with year and month (YYYYMM) into a table as inserts are made into another table.
Example:
As inserts are made into table 'original_table'
create table original_table
(opt_value char(2),
low_value varchar2(24),
high_value varchar2(24));
create table new_values
(id_values varchar2(24),
yr_month number(6));
Insert into original_table(opt_value,low_value,high_value) values ('EQ', '1111111111', '1111111111');
Insert into original_table(opt_value,low_value,high_value) values ('BT', '2222222000', '2222222999');
Insert into original_table(opt_value,low_value,high_value) values ('BT', '3333333350', '3333333399');
original_table
opt_value
low_value
high_value
EQ
1111111111
1111111111
BT
2222222000
2222222999
BT
3333333350
3333333399
Obs: Where EQ stands for 'equal' and BT 'between'. When 'EQ' just need to insert one of the values low or high don't matter, when 'BT' need to generate all the numbers between the two values and insert then into 'new_values' table.
table 'new_values' should get:
new_values
id_values
yr_month
1111111111
202111
2222222000
202111
2222222001
202111
2222222002
202111
...
...
2222222999
202111
3333333350
202111
3333333351
202111
...
...
3333333399
202111
I create a trigger which works, but i find it a little slow, and i don't like to use BEFORE INSERT statement, but can't use AFTER INSERT without getting mutating table error.
create or replace TRIGGER TRG_NAME
BEFORE INSERT
ON original_table
FOR EACH ROW
BEGIN
IF :NEW.opt_value = 'BT' THEN
INSERT INTO new_values (id_values, yr_month)
with tab123 (h_value, l_value, y_month)
as (select :NEW.high_value, cast(:NEW.low_value as number) , to_char(trunc(sysdate), 'YYYYMM')
from original_table
union all
select h_value, l_value +1, y_month
from tab123
where l_value < h_value)
select distinct l_value, y_month
from tab123;
ELSIF :NEW.opt_value = 'EQ' THEN
INSERT INTO new_values (id_values, yr_month) values
( :NEW.high_value, to_char(add_months(trunc(sysdate), -1), 'YYYYMM'));
END IF;
END;
Any tips in how to improve this code will be much appreciated.

Answer 1

You get a mutating table error, when you read from the table that is changing.
It's weird that you are getting it in an AFTER INSERT trigger and not with a BEFORE INSERT trigger. I would have assumed them to both result in the same error, because in both scenarios you read from the triggering table in your trigger. Well, this may have to do with only inserting one row. If you insert more rows at a time, you may get the error with both trigger variants.
In your case reading all the rows from the original_table in your trigger only produces duplicates anyway, that you fend off with DISTINCT. Instead, don't read from the table. It is not necessary. Read from DUAL instead, to get one row with the desired values:
with tab123 (h_value, l_value, y_month) as
(
select :new.high_value, cast(:new.low_value as number), to_char(sysdate, 'yyyymm')
from dual
union all
select h_value, l_value + 1, y_month
from tab123
where l_value < h_value
)
select l_value, y_month
from tab123;
This will get you rid of the mutating table error and also speed up the trigger.