How to Update value in one table by coping it from another table in plsql ? - oracle

Question

This is a simple example of what I need to do. In fact I want to Update value in one table by coping it from another table by using cursors in plsql.
I take table f and table b as two examples:
f=
1|Thom
2|Bob
3|Steven
5|Arthur
b=
7|Nataly
9|Alfred
, where I need to insert the b 's tow lines in first f two lines:
create table f (a number, b varchar2(10));
insert into f values (1,'Thom');
insert into f values (2,'Bob');
insert into f values (3,'Steven');
insert into f values (5,'Arthur');
commit;
create table b (c number, d varchar2(10));
insert into b values (7,'Nataly');
insert into b values (9,'Alfred');
commit;
create or replace procedure wco as
cursor c_f is
select a,b from f for update;
v_a f.a%type;
v_b f.b%type;
cursor c_b is
select c,d from b;
v_c b.c%type;
v_d b.d%type;
begin
open c_f;
open c_b
loop
fetch c_f into v_a, v_b;
exit when c_f%ROWCOUNT=c_b%RROWCOUNT;
update f set a=v_c and b=v_d where current of c_f;
end loop;
close c_d:
close c_f;
end;
/
exec wco;
select * from f;
drop table f;
The expected result (What i hope to have):
7|Nataly
9|Alfred
3|Steven
5|Arthur
But what I have now (as a result)is:
1|Thom
2|Bob
3|Steven
5|Arthur
How do I resolve this problem, I am a beginner with PLSQL, I would be very grateful if you could help me please.

Answer 1

Your procedure compiles, but with errors;
In order to see compilation errors
run show errors; after compilation.
Change open c_b to open c_b; (missing semicolon at the end)
Change close c_d: to close c_b; (correct name is c_b and semicolon instead of colon)
Change exit when c_f%ROWCOUNT=c_b%RROWCOUNT; to exit when c_f%ROWCOUNT=c_b%ROWCOUNT; (wrong %RROWCOUNT;)
update f set a=v_c and b=v_d where current of c_f; This is wrong SQL syntax.
Should be update table_name set column=value, column=value;
It is important to provide descriptive names to your variables, so it would be easier to understand your logic.
As I understood you want to copy only second two rows from source table.
create table source_table (
id number,
name varchar2(10));
/
insert into source_table values (1,'Thom');
insert into source_table values (2,'Bob');
insert into source_table values (3,'Steven');
insert into source_table values (5,'Arthur');
/
create table target_table (
id number,
name varchar2(10));
/
insert into target_table values (7,'Nataly');
insert into target_table values (9,'Alfred');
/
create or replace procedure copy_tables
AS
begin
FOR source_row IN (select id, name
from source_table
offset 2 rows)
LOOP
insert into target_table
values(source_row.id, source_row.name);
END LOOP;
end;
/
exec copy_tables;
/
select id, name from target_table;
/

Answer 2

You don't need PL/SQL for this; it can be achieved in a single MERGE statement:
merge into f tgt
using (select coalesce(b1.id, f1.id) id,
coalesce(b1.name, f1.name) name,
f1.f_rowid
from (select id,
name,
rowid f_rowid,
row_number() over (order by id) rn
from f) f1
full outer join (select id,
name,
row_number() over (order by id) rn
from b) b1
on f1.rn = b1.rn) src
on (tgt.rowid = src.f_rowid)
when matched then
update set tgt.id = src.id,
tgt.name = src.name
where tgt.id != src.id
or tgt.name != src.name
when not matched then
insert (tgt.id, tgt.name)
values (src.id, src.name);
See https://livesql.oracle.com/apex/livesql/file/content_FBPR7YCLFVWO7NGDXTLSP1R97.html for the test details (two examples; the target table has more and has fewer rows than the source table).
If you need to, you could add the above insert into a procedure, e.g.:
create procedure populate_target_table as
begin
merge into f tgt
using (select coalesce(b1.id, f1.id) id,
coalesce(b1.name, f1.name) name,
f1.f_rowid
from (select id,
name,
rowid f_rowid,
row_number() over (order by id) rn
from f) f1
full outer join (select id,
name,
row_number() over (order by id) rn
from b) b1
on f1.rn = b1.rn) src
on (tgt.rowid = src.f_rowid)
when matched then
update set tgt.id = src.id,
tgt.name = src.name
where tgt.id != src.id
or tgt.name != src.name
when not matched then
insert (tgt.id, tgt.name)
values (src.id, src.name);
end;
/