SQl Update from table of random Names

Question

I Have a table of random names, simply 3 columns(id, firstname, lastname).

I am trying to have SQL update an entire table of names

Answer 1

Here is the query:

update TestNames t cross join
       rndnames r
    set t.fname = r.FirstName,
        t.lname = r.LastName
    where r.ID = floor(1+(rand()*600));

It only updates a row in testnames when the random id chosen by the expression matches an id in the table. Are the id values in rndnames all populated?

If your table is not very big and it has an id, here is another approach:

update TestName t join
       (select t.*,
               (select id from rndnames order by rand() limit 1) as rndid
        from testname t
       ) tr
       on t.id = tr.id join
       rndnames r
       on t.rndid = r.id
    set t.fname = r.FirstName,
        t.lname = r.LastName;

EDIT:

I think this will also work:

update TestNames t cross join
       rndnames r
    set t.fname = r.FirstName,
        t.lname = r.LastName
    where r.ID = (select id
                  from rndnames
                  order by rand()
                  limit 1
                 );

Answer 2

update
TestNames left join 
(select ID,
floor(1+(rand()*600)) as rndid
from TestNames) as TN on TN.ID=TestNames.id
left join rndnames on TN.rndid=rndnames.id
set TestNames.fname=rndnames.FirstName,TestNames.lname=rndnames.LastName