SQL Server : combining COUNT(*) for different tables at once - sql

Question

I have a few queries that I would like to combine into ONE query in order to not have to call out to the server multiple times.
An example of the queries I am using:
SELECT COUNT(*) AS mailCount1
FROM [WebContact].[dbo].[memberEmails]
WHERE contactdatetime > '01/01/06'
AND contactdatetime < '02/01/06'
SELECT COUNT(*) AS mailCount2
FROM [WebContact].[dbo].[otherEmails]
WHERE contactdatetime > '01/01/06'
AND contactdatetime < '02/01/06'
SELECT COUNT(*) AS mailCount3
FROM [WebContact].[dbo].[memberEmails]
WHERE contactdatetime > '02/01/06'
AND contactdatetime < '03/01/06'
SELECT COUNT(*) AS mailCount4
FROM [WebContact].[dbo].[otherEmails]
WHERE contactdatetime > '02/01/06'
AND contactdatetime < '03/01/06'
etc etc...
So as the examples above, only thing that changes are:
The FROM (memberEmails & otherEmails)
The > & < months (01/01/06, 02/01/06 | 02/01/06, 03/01/06 | etc...)
Is this possible to do with a single query?

Answer 1

First, use group by and just use two queries:
select year(contactdatetime) as yyyy, month(contactdatetime) as mm, count(*)
from WebContact].[dbo].[memberEmails]
group by year(contactdatetime), month(contactdatetime);
and:
select year(contactdatetime) as yyyy, month(contactdatetime) as mm, count(*)
from WebContact].[dbo].[otherEmails]
group by year(contactdatetime), month(contactdatetime);
Then, if you like, you can combine these into a single query:
select coalesce(me.yyyy, oe.yyyy) as yyyy, coalesce(me.mm, oe.mm) as mm,
coalesce(me.cnt, 0) as memberemailcnt,
coalesce(oe.cnt, 0) as otheremailcnt
from (select year(contactdatetime) as yyyy, month(contactdatetime) as mm, count(*) as cnt
from WebContact].[dbo].[memberEmails]
group by year(contactdatetime), month(contactdatetime)
) me full outer join
(select year(contactdatetime) as yyyy, month(contactdatetime) as mm, count(*) as cnt
from WebContact].[dbo].[otherEmails]
group by year(contactdatetime), month(contactdatetime)
) oe
on me.yyyy = oe.yyyy and me.mm = oe.mm;
A full outer join is not necessary if both tables have data for all months.

Answer 2

declare #emailCount table(tablename varchar(20), year int, month int, qty int)
insert into #emailCount
select 'memberEmails', year(contactdatetime), month(contactdatetime), count(*)
from [WebContact].[dbo].[memberEmails]
group by year(contactdatetime), month(contactdatetime)
insert into #emailCount
select 'otherEmails',year(contactdatetime), month(contactdatetime), count(*)
from [WebContact].[dbo].[otherEmails]
group by year(contactdatetime), month(contactdatetime)
select tablename, year, month, qty from #emailCount
Add WHERE clause if needed to restrict date ranges. (edit- simplified to use year() and month() functions.)

Answer 3

I haven't check the syntax or performance but you can do something like this,
WITH cte (
countvalue
,description
)
AS (
SELECT COUNT(*)
,'mailCount1'
FROM [WebContact].[dbo].[memberEmails]
WHERE contactdatetime > '01/01/06'
AND contactdatetime < '02/01/06'
UNION ALL
SELECT COUNT(*)
,'mailCount2'
FROM [WebContact].[dbo].[otherEmails]
WHERE contactdatetime > '01/01/06'
AND contactdatetime < '02/01/06'
UNION ALL
SELECT COUNT(*)
,'mailCount3'
FROM [WebContact].[dbo].[memberEmails]
WHERE contactdatetime > '02/01/06'
AND contactdatetime < '03/01/06'
UNION ALL
SELECT COUNT(*)
,'mailCount4'
FROM [WebContact].[dbo].[otherEmails]
WHERE contactdatetime > '02/01/06'
AND contactdatetime < '03/01/06'
)
SELECT mailCount1
,mailCount2
,mailCount3
,mailCount4
FROM (
SELECT countvalue
,description
FROM cte
) d
pivot(max(countvalue) FOR description IN (mailCount1, mailCount2, mailCount3, mailCount4)) piv;
Hope this helps..