Postgres查询等价

Question

我想知道这两个查询是否产生相同的结果：

    update A.cred
set user_name = concat(CURRENT_TIMESTAMP::text)
from A.temp_table2 tt
WHERE email NOT IN (select email from A.temp_table2 it
join A.cred c on c.user_name = it.email
join A.at a on a.ld = c.ld
join A.ap ar on ar.cd = a.ad)
AND tt.email = A.cred.user_name


    update A.cred c
join A.temp_table t on t.email = c.user_name
set user_name = concat(CURRENT_TIMESTAMP::text)
WHERE c.user_name NOT IN (select t.email from A.temp_table2 t
join A.cred c on c.user_name = t.email
join A.at a on a.ld = c.ld
join A.ap ar on ar.cd = a.ad)

另外，如果有人能向我解释为什么一个比另一个好，请为我列举一下。