Use of HAVING without GROUP BY in SQL queries
No.

They don't have to coexist, as proved by the fact that the following query in Oracle works:

select * from dual having 1 = 1;


Similarly, in PostgreSQL the following query works:

select 1 having 1 = 1;


So having doesn't require group by.

Having is applied after the aggregation phase and must be used if you want to filter aggregate results. So the reverse isn't true, and the following won't work:

select a, count(*) as c
from mytable
group by a
where c &gt; 1;


You need to replace where with having in this case, as follows:

select a, count(*) as c
from mytable
group by a
having c &gt; 1;


NB The following query form will also work:

select *
from (
  select a, count(*) as c
  from mytable
  group by a
)
where c &gt; 1;


You can see that using having is simply a shorthand version of this last query.



In summary, having is applied after the group by phase whereas where is applied before the group by phase.