Error while using same table data twice during inner join - sql

Question

Suppose I have a table, in Database name 'Old', as below:
TABLE A
(
SeniorVehicle varchar(255),
SeniorVehicleAllowance int,
JuniorVehicle varchar(255),
JuniorVehicleAllowance int
ManagerVehicle varchar(255),
ManagerVehicleAllowance int
);
And another table, in Database name 'New' as below:
TABLE B
(
SeniorVehicle int,
SeniorVehicleAllowance int,
JuniorVehicle int,
JuniorVehicleAllowance int,
ManagerVehicle int,
ManagerVehicleAllowance int
);
I want to bring the data from TABLE A of Database 'Old' to TABLE B of Database 'New'.
The thing is that, there is a table named Vehicle in both databases as bellow:
TABLE Vehicle
(
VehicleID int pk,
VehicleName varchar(255)
)
Values in SeniorVehicle, JuniorVehicle and ManagerVehicle columns in TABLE A are the VehicleName value in TABLE Vehicle. But the value of SeniorVehicle, JuniorVehicle and ManagerVehicle that must be stored in TABLE B must be the value of VehicleID column in the Vehicle Table.
How to achieve this without error????
I have tried the following:
INSERT INTO B
(SeniorVehicle, SeniorVehicleAllowance, JuniorVehicle, JuniorniorVehicleAllowance, ManagerVehicle, ManagerVehicleAllowance)
SELECT Vehicle.VehicleID, c.SeniorVehicleAllowance, c.VehicleID, c.JuniorVehicleAllowance, c.VehicleID, c.ManagerVehicleAllowance
FROM (SELECT b.SeniorVehicle, b.SeniorVehicleAllowance, Vehicle.VehicleID, b.JuniorVehicleAllowance, b.VehicleID, b.ManagerVehicleAllowance
FROM (SELECT a.SeniorVehicle, a.SeniorVehicleAllowance, a.JuniorVehicle, a.JuniorVehicleAllowance, Vehicle.VehicleID, a.ManagerVehicleAllowance
FROM (SELECT SeniorVehicle, SeniorVehicleAllowance, JuniorVehicle, JuniorVehicleAllowance, ManagerVehicle, ManagerVehicleAllowance FROM A) as a
Inner join
Vehicle
ON a.ManagerVehicle = Vehicle.VehicleName) as b
Inner join
Vehicle
ON b.JuniorVehicle = Vehicle.VehicleName) as c
Inner join
Vehicle
ON c.SeniorVehicle = Vehicle.VehicleName
I get the following error:
The column 'VehicleID' was specified multiple times for 'c'
My Databse is MSSQL Server 2008 R2

Answer 1

Reformatting your current query gives:
SELECT
Vehicle.VehicleID,
c.SeniorVehicleAllowance,
c.VehicleID,
c.JuniorVehicleAllowance,
c.VehicleID,
c.ManagerVehicleAllowance
FROM (
SELECT b.SeniorVehicle,
b.SeniorVehicleAllowance,
Vehicle.VehicleID,
b.JuniorVehicleAllowance,
b.VehicleID,
b.ManagerVehicleAllowance
FROM (
SELECT a.SeniorVehicle,
a.SeniorVehicleAllowance,
a.JuniorVehicle,
a.JuniorVehicleAllowance,
Vehicle.VehicleID,
a.ManagerVehicleAllowance
FROM (
SELECT SeniorVehicle,
SeniorVehicleAllowance,
JuniorVehicle,
JuniorVehicleAllowance,
ManagerVehicle,
ManagerVehicleAllowance
FROM A
) as a
Inner join Vehicle
ON a.ManagerVehicle = Vehicle.VehicleName
) as b
Inner join Vehicle
ON b.JuniorVehicle = Vehicle.VehicleName
) as c
Inner join Vehicle
ON c.SeniorVehicle = Vehicle.VehicleName
In this query, the sub query aliased c has two columns called VehicleID (which is what your error message is telling you.
The smallest change to fix the issue is to alias the columns in the sub query, e.g:
SELECT
Vehicle.VehicleID AS SeniorVehicleId,
c.SeniorVehicleAllowance,
c.JuniorVehicleId,
c.JuniorVehicleAllowance,
c.ManagerVehicleID,
c.ManagerVehicleAllowance
FROM (
SELECT b.SeniorVehicle,
b.SeniorVehicleAllowance,
Vehicle.VehicleID AS JuniorVehicleId,
b.JuniorVehicleAllowance,
b.ManagerVehicleID,
b.ManagerVehicleAllowance
FROM (
SELECT a.SeniorVehicle,
a.SeniorVehicleAllowance,
a.JuniorVehicle,
a.JuniorVehicleAllowance,
Vehicle.VehicleID AS ManagerVehicleID,
a.ManagerVehicleAllowance
-- Rest ommited for brevity
It would be also possible to re-write the query with more joins, and omit the need for the subqueries altogether also:
SELECT srmgr.VehicleId AS SeniorVehicleId,
A.SeniorVehicleAllowance,
jrmgr.VehicleId AS JuniorVehicleId,
A.JuniorVehicleAllowance,
mgr.VehicleId AS ManagerVehicleId,
A.ManagerVehicleAllowance
FROM A
INNER JOIN Vehicle AS mgr
ON a.ManagerVehicle = mgr.VehicleName
INNER JOIN Vehicle AS jrmgr
ON a.ManagerVehicle = jrmgr.VehicleName
INNER JOIN Vehicle AS srmgr
ON a.ManagerVehicle = srmgr.VehicleName