SQL Select within a select - sql

Question

I'm creating a dataset that will be displayed in an SSRS report.
I have a query in a job that puts a count into a table [dbo].[CountMetersDue] on a rolling basis on the 1st of every month; the value changes throughout the month so need to take a snapshot at beginning.
I have the report set up which uses a custom expression to produce a cumulative trend graph. Basically takes one value, divides by another to work out a percentage. Therefore I have two queries that need combining... Took me ages to get my head round all this!
I just need help with the last bit.
SELECT (SELECT [Count]
FROM [MXPTransferDev].[dbo].[CountMetersDue]
WHERE [MXPTransferDev].[dbo].[CountMetersDue].[DateTime] =
[MXPTransferDev].[dbo].[Readings].[dateRead]) AS [MetersDue],
COUNT(readingid) AS [TotalReadings],
CONVERT(DATE, dateread) AS [dateRead]
FROM [MXPTransferDev].[dbo].[Readings]
WHERE ( [MXPTransferDev].[dbo].[Readings].[dateRead] BETWEEN
'01-may-11' AND '31-may-11' )
AND ( webcontactid IS NOT NULL )
AND ( meter = 1 )
GROUP BY CONVERT(DATE, [MXPTransferDev].[dbo].[Readings].[dateRead])
CREATE TABLE [dbo].[CountMetersDue](
[Count] [int] NULL,
[DateTime] [datetime] NULL
) ON [USER]
GO
ALTER TABLE [dbo].[CountMetersDue]
ADD CONSTRAINT [DF_CountMetersDue_DateTime] DEFAULT (getdate()) FOR [DateTime]
GO
CREATE TABLE [dbo].[Readings](
[readingId] [bigint] IDENTITY(1,1) NOT FOR REPLICATION NOT NULL,
[dateRead] [datetime] NOT NULL,
[meter] [int] NOT NULL,
[webcontactid] [bigint] NULL,
Readings
readingId meter reading dateRead webcontactid
583089 4 3662 2011-05-25 15:00:33.040 479
583207 3 682 2011-05-25 15:00:33.027 479
583088 2 98064 2011-05-25 15:00:33.007 479
CountMetersDue
Count DateTime
2793 2011-12-01 00:00:00.000
1057 2011-05-01 14:08:20.437
610 2011-03-01 00:00:00.000

Answer 1

Second stab at answering your question (will probably need some clarification from yourself before the answer is correct):
/* DDL: 2 tables [CountMetersDue] & [Readings]
[CountMetersDue]
([DateTime] datetime,
[Count] int)
[Readings]
([ReadingId] bigint,
[dateRead] datetime,
[webcontactid] bigint,
[meter] int)
[CountMetersDue] - contains 1 record on the first of every month, with count of the number of readings at that date
[Readings] - contains all the individual readings
ie:
[CountMetersDue]
01-Jan-2011 1000
01-Feb-2011 2357
01-Mar-2011 3000
[Readings]
1 01-Jan-2011 11 1
2 02-Jan-2011 12 1
3 03-Jan-2011 13 1
...
*/
SELECT
CONVERT(DATE, [dbo].[Readings].[dateRead]) AS dateRead,
COUNT([dbo].[Readings].[readingId]) AS TotalReadings,
[dbo].[CountMetersDue].[Count] AS MetersDue
FROM
[CountMetersDue] /* get all count meters due */
left join [Readings] /* get any corresponding Reading records
where the dateRead in the same month as
the CountMetersDue */
on DATEPART(year, Readings.dateRead) = DATEPART(year, [CountMetersDue].[DateTime]) /* reading in same year as CountMetersDue */
and DATEPART(month, Readings.dateRead) = DATEPART(month, [CountMetersDue].[DateTime]) /* reading in same month as CountMetersDue */
WHERE ([MXPTransferDev].[dbo].[Readings].[dateRead]) BETWEEN
#StartDate AND #EndDate
AND ( webcontactid IS NOT NULL )
AND ( meter = 1 )
GROUP BY
[dbo].[CountMetersDue].[Count],CONVERT(DATE, [dbo].[Readings].[dateRead])

Answer 2

This would be the query you are looking for then?
Subqueries, as they are called, can be included by enclosing them in parentheses '()'.
SELECT (SELECT [Count] FROM [xxxxx].[dbo].[CountMetersDue] AS tabA WHERE tabA.[datefield] = tabB.dateRead) AS [MetersDue], COUNT(readingId) AS [TotalReadings], CONVERT(DATE, dateRead) AS [dateRead]
FROM [xxxxx] AS tabB
WHERE (dateRead BETWEEN #StartDate AND #EndDate) AND (webcontactid IS NOT NULL) AND (meter = 1)
GROUP BY CONVERT(DATE, dateRead)