Splitting and inserting a string in PL/SQL - sql

Question

I have a table called LOG that has a column named MESSAGE, which is a VARCHAR2(4000).
Since I'm planning a migration and the column MESSAGE in the new database is a VARCHAR2(2000), I want to iterate over all MESSAGE rows with length > 2000 and substring the text after 2000 characters and insert everything of the text that comes after 2000 characters into a new row.
I also have to update the original rows to have 2000 chars.
How can I do this? It's been really a long time since I worked with PL/SQL, I would really appreciate your help.

Answer 1

It can also easily be done with a connect by as it demonstrates in this example where it should split after every 5th character:
select substr(test.test, (level-1)*5, 5)
from (select 'THIS IS A LONG MESSAGE ACTUALLY' test from dual) test
connect by substr(test.test, (level-1)*5, 5) IS NOT NULL
in this scenario you wouldn´t even have to bother about anything at it would automaticly seperate the values no matter if they are longer than 2000 or not.
select substr(l.message, (level-1)*2000, 2000) message
from log l
substr(l.message, (level-1)*2000, 2000) IS NOT NULL
This could be your final select.

Answer 2

One method is:
select . . ., substr(l.message, 1, 2000) as message
from log l
union all
select . . ., substr(l.message, 2001, 2000) as message
from log l
where lenght(l.message) > 2000;

Answer 3

Your problem can be solved using a PLSQL block as below. Please try to implement the logic mentioned inline and check if this works.
Code:
declare
---getting each message of length 4000 characters
cursor cur is
select message
from log;
var number;
var1 varchar2(2000);
cntr number:=0;
begin
--Loop for each message
for i in cur
loop
--getting length of message
var:= length(i.message);
for len in 1..(var / 2000)
loop
--setting the offset to pick 2000 chracters
if cntr = 0 then
cntr := cntr +1;
else
cntr := cntr + 2000;
end if;
--selecting 2000 characters from message
var1:=substr(i.message,cntr,2000);
---inserting 2000 charcters to table
insert into table_log(col1)
values(var1 );
commit;
end loop;
end loop;
end;
Demo:
SQL> create table log(message varchar2(4000));
SQL> select message from log ;
MESSAGE
--------------------------------------------------------------------------------
KHAGDKAGDHAGDKHAGD
ADSJHA:DAH:DHHAHDH
.
.
.
SQL> select length(message) from log ;
LENGTH(MESSAGE)
---------------
3989
SQL> create table table_log(col1 varchar2(2000));
SQL> select col1 from table_log ;
COL1
--------------------------------------------------------------------------------
SQL> /
PL/SQL procedure successfully completed.
--- Two rows created to destination table with size approx 2000 characters each
SQL> select length(col1) from table_log ;
LENGTH(COL1)
------------
2000
1989
In Simple SQL you can do it as
insert into table_log(col1)
select SUBSTR(l.MESSAGE, 1, 2000) AS MESSAGE
FROM LOG l
UNION ALL
select SUBSTR(l.MESSAGE, 2001, 2000) AS MESSAGE
FROM LOG l
WHERE length(l.MESSAGE) > 2000;

Answer 4

You can split rows during copying to new table. For this you should use INSERT ALL WHEN. For each WHEN clause whose condition evaluates to true, the database executes the corresponding INTO clause list.
create table src_test_table(long_msg varchar2(20));
create table dest_test_table(long_msg varchar2(10));
insert into src_test_table values(lpad('1',20,'1'));
insert into src_test_table values(lpad('2',20,'2'));
insert into src_test_table values(lpad('3',20,'3'));
insert into src_test_table values(lpad('4',10,'4'));
insert into src_test_table values(lpad('5',10,'5'));
insert all
when length(long_msg) <= 10 then
into dest_test_table values(long_msg)
when length(long_msg) > 10 then
into dest_test_table values(substr(long_msg,1,10))
when length(long_msg) > 10 then
into dest_test_table values(substr(long_msg,11))
select long_msg from src_test_table;
And results;
select long_msg,length(long_msg) from dest_test_table;