Web Developers → mySql return selected fields in select when using if exists

When using if exists with a select, how can I get it to return the id or what ever field or fields I want it to display, or 'Does not exist'?

SELECT IF(EXISTS( SELECT id, dateIn FROM table WHERE id = 10), my selected fields here, 'Does not exist')
 

Or is there's another way to do this?

select
case when id is not null then id else 'n/a' end as id,
case when datein is not null then datein else 'n/a' as datein
from mytable
where...

id will not be NULL. If it doesn't exist, it's just blank. Can something like this be done?

select
case when exists (id) then id else 'n/a' end as id
from mytable
where id="35";
 

Exists requires a subquery, which you have, but a blank will be considered a value so exists will always be true on blanks. Think of 'exists' as 'there is a row matching the criteria'. To map blanks/nulls to user friendly values, you will need to use CASE or COALESCE.

2 options:

SELECT
  CASE
    WHEN id = '' THEN 'n/a'
    ELSE id
  END
FROM mytable;
 

or

SELECT
   COALESCE(NULLIF(id,''), 'n/a') AS 'id'
FROM mytable;
 

**edits... brain farts on code blocks.

So I did:

SELECT
  CASE
    WHEN id = '' THEN 'n/a'
    ELSE id
  END
FROM mytable where id = 10;
 

If id exists all is fine, but if not I don's see 'n/a'

is there a row with id=10?

Yes there is. It works fine if a row exists. If there isn't one I don't get the 'N/A' message. That's the strangest part.

I didn't realize it's the ID field itself where you put the condition - in such a case it would only return that id and nothing else (no null, no blank).
It might be easier to use a subquery/temp table to make the decision

declare @resultstbl table (id varchar, datein datetime)
declare @numrecords int
insert into @resultstbl (id, datein) select id, datein from mytable where...
select @numrecords = count(*) from @resultstbl
if @numrecords>0
select id, datein from @resultstbl
else
select 'no record' as id, 'n/a' as datein