How to update multiple values in oracle? - oracle

Question

I have two tables:
table 1:
|Project type|Quarter1|Quarter2|Quarter3|Quarter4|
|------------|--------|--------|--------|--------|
|type1 |1 |3 |5 |7 |
|type2 |2 |4 |6 |8 |
table 2:
|Project|Value|Quarter|
|-------|-----|-------|
|type1 | |1 |
|type2 | |1 |
|type1 | |2 |
|type2 | |2 |
|type1 | |3 |
|type2 | |3 |
|type1 | |4 |
|type2 | |4 |
I want to update table 2 value section with data from table 1 and the expected outcome is:
|Project|Value|Quarter|
|-------|-----|-------|
|type1 |1 |1 |
|type2 |2 |1 |
|type1 |3 |2 |
|type2 |4 |2 |
|type1 |5 |3 |
|type2 |6 |3 |
|type1 |7 |4 |
|type2 |8 |4 |
I know updating single one value can be written as:
update table2 a
set a.value = (select Quarter1
from table1
where projecttype = 'type1')
where a.project = 'type1'
and a.quarter = '1';
Please tell me how can I update all value in one time?
Thank you!

Answer 1

One way is with a merge statement:
merge into table_2 t
using table_1 s
on (t.project = s.project_type)
when matched then update
set t.value = case t.quarter when 1 then s.quarter1
when 2 then s.quarter2
when 3 then s.quarter3
when 4 then s.quarter4 end
;

Answer 2

This is my primary thought about using loop to repeat the updating process. The main body refer to mathguy's answer (Thanks again). It may complicate the code in this scenario, but would be useful when there are numerous columns in table1, such as years instead quarters.
declare
quart_num number;
code varchar2(2000);
begin
for quart_num in 1..4
loop
code := 'merge into table2 a
using table1 b
on (a.project = b.projecttype)
when matched then
update set a.value = quarter'||
quart_num || 'where a.quarter =' ||quart_num;
execute immediate(code);
end loop;
end;