Oracle Updates another table field with one table field three ways ____oracle

1. Update (SELECT ..... ) Set column1 = Column2;

Update (select Iy.company_name company_name1, CC.COMPANY_NAME_JC company_name2
From Income_year_item iy, City_company cc

where Iy.company_code = Cc.code
)
Set company_name1 = Company_name2;

2. Only single-line subquery s

Update City_project_scale_info C Set
(c.value) = (
Select D.value from City_project_scale_info @test d where d.project_id = ' 7d7fd580a06240b2a9137dc2bbe831e9 '
and d.project_id = c.project_id and C.company_code = D.company_code
)
where exists (
Select 1 from City_project_scale_info @test d where d.project_id = ' 7d7fd580a06240b2a9137dc2bbe831e9 '
and d.project_id = c.project_id and C.company_code = D.company_code
)

3. Use Merg inot statement

--Update Production base fields
Merge into City_cfg_data_column_common CF1 using
City_cfg_data_column_common2 CF2 on
(Cf1.resourceid = Cf2.resourceid)
When matched then
Update Set cf1.template_type = Cf2.template_type,
Cf1.chinese_name = Cf2.chinese_name,
Cf1.column_name = Cf2.column_name,
Cf1.column_type = Cf2.column_type,
Cf1.column_size = Cf2.column_size
When not matched then
Insert (cf1.resourceid,cf1.template_type,cf1.chinese_name,cf1.column_name,cf1.column_type,cf1.column_size
, Cf1.is_can_edit,cf1.is_unique,cf1.is_can_cover,cf1.show_order)
VALUES (cf2.resourceid,cf2.template_type,cf2.chinese_name,cf2.column_name,cf2.column_type,cf2.column_size
, Cf2.is_can_edit,cf2.is_unique,cf2.is_can_cover,cf2.show_order)