Let’s say we have a couple of simple SQL queries, one of which counts the total number of job hours:

select sum(Hours) as totalCount from job_details where Job_ID = 42504;

and another query that sums the total number of job hours that have been completed:

select sum(Hours) as completedCount from job_details where Job_ID = 42504 and Completed = 1;

If we want to combine both of these queries into a single query, we can! The trick is to use aliases for both of the selects.

For example, here I have used the aliases “as a” and “as b”:

select 
    totalCount, 
    completedCount 
from 
    (select sum(Hours) as totalCount from job_details where Job_ID = 42504) as a, 
    (select sum(Hours) as completedCount from job_details where Job_ID = 42504 and Completed = 1) as b;

Here is an example of wrapping 5 SQL queries into one:

select 
	total, 
	completed, 
	dept_id, 
	deptName,
	schedStart,
	schedEnd,
	numTasks
from 
	(select 
		sum(details.Hours) as total 
	from 
		job_details details, 
		job_schedule sched
	where 
		details.Job_ID = '41230' and
		sched.Shop_ID = '9553' and
		details.Job_ID = sched.Job_ID) as a,

	(select 
		sum(details.Hours) as completed 
	from 
		job_details details, 
		job_schedule sched
	where 
		details.Job_ID = '41230' and 
		details.Completed = 1 and
		sched.Shop_ID = '9553' and
		details.Job_ID = sched.Job_ID) as b,

	(select 
		store.Dept_ID as dept_id, 
		website.Department as deptName 
	from 
		store.job_details store, 
		job_schedule sched,
		website.customer_service_department website 
	where 
		store.Job_ID = '41230' and 
		sched.Shop_ID = '9553' and
		store.Completed = 0 and 
		store.Dept_ID = website.ID and
		store.Job_ID = sched.Job_ID) as c,

	(select 
		Scheduled_Start as schedStart,  
		Scheduled_End as schedEnd
		from job_schedule sched
	where 
		Job_ID = '41230' and 
		Shop_ID = '9553') as d,

	(select 
		count(Description) as numTasks 
	from 
		job_details 
	where 
		Job_ID = '41230') as e;

Notes:

• Each of the columns in the output are listed in the inital select at the top of the overall query. For example, the first column “total” is returned by the first query “a”.
• In the FROM portion of the overall query, there are 5 sub-queries, with aliases a – e.
• Each sub-query starts with select and is wrapped in parenthesis.
• The output of each sub-query feeds the top level selects.
• It is possible for a sub-query to return more than one output. For example sub-query c returns both dept_id and deptName.