how does update work with 'not in'

[Johnny JL]

sample:

update tableA 
   set flag = 'N' 
where id not in 
   (select id 
    from tableA 
    where flag = 'Y')

Q: how does this query work?
is system firstly get the list which falg is 'Y', then pick up each id and check if it's in the list, then update accordingly?

Or

is system pick up one id and get the list which flag is 'Y' everytime, then update accordingly?

[ck9663]

It sounds like it is...


~~ CK

[Rabbit]

I don't understand either one of your descriptions. What it's doing is if an id has a record in the table where the flag is set to Y, don't update that row. Update everything else to N.

[chetan9529]

First statement is correct. firstly get the list which falg is 'Y'. then will check with all id's..