insert into new column values generated from trigger - oracle

Question

I want to create a trigger which generates an 18 digit code based on the value of several other columns in the table.
R-MU-WEST-RJS-9697 So basically my last 4 digit code is the STORE_CODE based on which I want to compare and insert that 18 digit code against it the column named as CODE_18DIGIT
Below is the select statement that generates the code
SELECT 'R-'
|| CASE
WHEN INSTR (TRIM (r.state), ' ') > 1
THEN
SUBSTR (r.state, 1, 1)
|| SUBSTR (r.state, INSTR (r.state, ' ') + 1, 1)
ELSE
UPPER (SUBSTR (r.state, 1, 2))
END
|| '-'
|| UPPER (SUBSTR (r.zone_name, 1, 4))
|| '-'
|| r.format_code
|| '-'
|| SUBSTR (r.store_code, 1, 4)
FROM tbl_rrsoc_store_info r
WHERE r.ISACTIVE = 'Y';
and the table description of tbl_rrsoc_store_info is below
Name Null Type
--------------------------- -------- --------------
RRSOC_ID NOT NULL NUMBER
STORE_CODE NOT NULL NVARCHAR2(55)
STATE NVARCHAR2(55)
CITY NVARCHAR2(55)
CODE_18DIGIT NVARCHAR2(18)

Answer 1

Architecturally, this is not a particularly good design. You're violating basic rules of normalization by storing redundant data. It would be much less objectionable to just create a view that computes the code or to add a computed column to the table instead. But it sounds like you have decided that you want to use the trigger-based solution.
For simplicity, I'd create a function (note that the code you posted references multiple columns that don't exist in the table definition you posted. My guess is that the columns exist and were omitted from your table definition but maybe you changed the column names in either your query or your table definition and didn't change them in the other).
create or replace function make_18digit_code(
p_state tbl_rrsoc_store_info.state%type,
p_zone_name tbl_rrsoc_store_info.zone_name%type, -- Note that your table definition doesn't include this column
p_format_code tbl_rrsoc_store_info.format_code%type, -- Or this column
p_store_code tbl_rrsoc_store_info.store_code%type
)
return tbl_rrsoc_store_info.code_18digit%type
is
begin
return 'R-' ||
CASE
WHEN INSTR (TRIM (p_state), ' ') > 1
THEN
SUBSTR (p_state, 1, 1)
|| SUBSTR (p_state, INSTR (p_state, ' ') + 1, 1)
ELSE
UPPER (SUBSTR (p_state, 1, 2))
END
|| '-'
|| UPPER (SUBSTR (p_zone_name, 1, 4))
|| '-'
|| p_format_code
|| '-'
|| SUBSTR (p_store_code, 1, 4);
end;
Then you can simply call the function in the trigger
create or replace trigger trg_generate_code
before insert or update on tbl_rrsoc_store_info
for each row
begin
:new.code_18digit := make_18digit_code( :new.state,
:new.zoe_name,
:new.format_code,
:new.store_code );
end;