SQL查询以获取唯一列表

Question

I have a table named 'resources'

Machine     Host        Enabled
mach1       host1       TRUE
mach2       host1       FALSE
mach3       host1       FALSE
mach4       host2       TRUE
mach5       host2       TRUE

I want to get the list of hosts where Enabled is True for all the resources/machines associated with them.

I tried the sql query-

select distinct Host from resources where Enabled = TRUE;

But that query gives me back both host1 and host2 as the answer whereas I am expecting the answer to be just host2. Can anyone help me with a sql query which can achieve this ?

Answer 1

Try this:

SELECT Host
FROM resources
GROUP BY Host        
HAVING COUNT(*) = COUNT(CASE WHEN Enabled = True THEN 1 END)

or:

SELECT DISTINCT Host 
FROM resources AS r1
WHERE Enabled = TRUE AND 
      NOT EXISTS (SELECT 1 
                  FROM resources AS r2
                  WHERE r1.Host = r2.Host AND r2.enabled = FALSE)

Answer 2

TRY THIS ONE AND LET ME KNOW.

SELECT DISTINCT(Host)
FROM Resources
WHERE Enabled = TRUE AND Host NOT IN (Select Host FROM Resources WHERE Enabled = FALSE)

Answer 3

Try

select distinct Host from resources res1 where not exist (
   select 1 from resources res2 WHERE res1.host = res2.host AND Enabled = FALSE limit 1
);

Answer 4

This works too

select host from resources e
having count(e.host)=(select count(enebled) from resources 
                    where enebled='TRUE' and host = e.host)
group by host;