SQL How to convert this to a SubQuery? - sql

Question

Learning, be kind.
I am trying to understand how this works and I have done several successful conversions, but this one I am stumped on.
How do I take this code and convert it to a subquery? I'm a little lost.
SELECT o.FirstName + ' ' + o.LastName AS Driver, COUNT(DISTINCT s.vehicleID) NoOfBusesUsed
FROM Operators AS o, Runs AS r, Schedules AS s JOIN Trips AS t
ON s.scheduleID = t.scheduleID
WHERE r.BidDate BETWEEN '09/01/2004' AND '09/30/2004'
GROUP BY o.FirstName + ' ' + o.LastName
HAVING COUNT(s.vehicleID) > 1
Here is how my tables are setup. If more info is needed, I can post.
CREATE TABLE Operators
(
SeniorityNumber char(4) NOT NULL
CONSTRAINT ck_Operators_Seniority
CHECK (SeniorityNumber LIKE '[0-9][0-9][0-9][0-9]'),
FirstName varchar(25) NOT NULL,
LastName varchar(35) NOT NULL,
HireDate smalldatetime
CONSTRAINT ck_Operators_HireDate CHECK (HireDate <=Getdate())
)
CREATE TABLE Trips
(
RouteNumber varchar(4) NOT NULL,
StartLocation varchar(50) NOT NULL,
StartTime time NOT NULL,
EndLocation varchar(50) NOT NULL,
EndTime time NOT NULL,
EffectiveDate smalldatetime NOT NULL
CHECK (EffectiveDate >= cast('1/1/2000' as smalldatetime)),
CONSTRAINT ck_Trips_StartEnd CHECK (EndTime > StartTime)
)
CREATE TABLE Vehicles
(
Manufacturer varchar(50)
DEFAULT 'Gillig',
Model varchar(50),
ModelYear int
DEFAULT DatePart(yyyy,GetDate())
CHECK (ModelYear <= DatePart(yyyy,GetDate())),
PurchaseDate smalldatetime
)
GO
ALTER TABLE operators
ADD OperatorID int IDENTITY --Primary Key
GO
ALTER TABLE Operators
ADD CONSTRAINT pkOperators Primary key (OperatorID)
ALTER TABLE Vehicles
ADD VehicleID int IDENTITY Primary Key
ALTER TABLE Trips
ADD TripID int IDENTITY Primary key
GO
CREATE TABLE Runs
(
RunID int IDENTITY NOT NULL Primary Key,
OperatorID int NOT NULL REFERENCES Operators,
BidDate date NOT NULL
CONSTRAINT ckRunBidDate CHECK
(biddate <= dateadd(mm,6,getdate())) --getdate() + 180
)
GO
CREATE TABLE Schedules
(
ScheduleID int IDENTITY Primary Key,
RunID int NOT NULL,
VehicleID int NOT NULL,
CONSTRAINT fk_Schedules_Runs FOREIGN KEY (RunID)
REFERENCES Runs(RunID),
CONSTRAINT fk_Schedules_Vehicles FOREIGN KEY (VehicleID)
REFERENCES Vehicles
)
ALTER TABLE Trips
ADD ScheduleID int NULL REFERENCES Schedules

Answer 1

When you want to use a query as a sub-query you can use WITH statement or a derived table like:
With:
;WITH subQuery AS (
/* Your query here */
)
SELECT *
FROM subQuery
Derived table
SELECT *
FROM (
/* your query here */
) As subQuery
I think you should use a query like this:
SELECT
o.FirstName + ' ' + o.LastName AS Driver,
DT.cnt AS NoOfBusesUsed
FROM
Operators AS o
JOIN
(SELECT
r.OperatorID,
COUNT(DISTINCT s.VehicleID) AS cnt
FROM
Schedules s
JOIN
Runs r ON s.RunID = r.RunID
) AS DT
ON DT.OperatorID = o.OperatorID
WHERE
ISNULL(DT.cnt, 0) > 1