In Oracle SQL, Add max values (row by row) from another table when other columns of the table are already populated - sql

Question

I have two tables A and B. Table B has 4 columns(ID,NAME,CITY,COUNTRY), 3 columns has values and one column (ID) has NULLS. I want to insert max value from table A column ID to table B where the ID field in B should be in increasing order.
Screenshot
TABLE A
ID NAME
------- -------
231 Bred
134 Mick
133 Tom
233 Helly
232 Kathy
TABLE B
ID NAME CITY COUNTRY
------- ------- ---------- -----------
(NULL) Alex NY USA
(NULL) Jon TOKYO JAPAN
(NULL) Jeff TORONTO CANADA
(NULL) Jerry PARIS FRANCE
(NULL) Vicky LONDON ENGLAND
ID in column in B should be populated as MAX(ID) +1 from table A. The output should look like this:
TABLE B
ID NAME CITY COUNTRY
------ -------- ---------- -----------
234 Alex NY USA
235 Jon TOKYO JAPAN
236 Jeff TORONTO CANADA
237 Jerry PARIS FRANCE
238 Vicky LONDON ENGLAND

Answer 1

Perhaps the simplest method is to create a one-time sequence for the update:
create sequence temp_b_seq;
update b
set id = (select max(id) from a) + temp_b_seq.nextval;
drop sequence temp_b_seq;
You could actually initialize the sequence with the maximum value from a, but that requires dynamic SQL, so this seems like the simplest approach. Oracle should be smart enough to run the subquery only once.