Oracle SQL：在'WITH'语句中，如何进行条件选择，使用IF还是CASE？

I have two tables:

我有两张桌子：

CREATE TABLE Test_Persons_A (
    PersonID int,
    LastName varchar(255),
    FirstName varchar(255)
);

INSERT INTO Test_Persons_A
    (PersonID,LastName,FirstName)
    values(11,'LN_A1','FN_A1');

INSERT INTO Test_Persons_A
    (PersonID,LastName,FirstName)
    values(12,'LN_A2','FN_A2');

CREATE TABLE Test_Persons_B (
    PersonID int,
    LastName varchar(255),
    FirstName varchar(255)
);

INSERT INTO Test_Persons_B
    (PersonID,LastName,FirstName)
    values(21,'LN_B1','FN_B1');

INSERT INTO Test_Persons_B
    (PersonID,LastName,FirstName)
    values(22,'LN_B2','FN_B2');

commit;
CREATE TABLE Te