How to do multiple left joins in SQL Server SQL Query - sql

Question

I'm trying to perform the query below on SQL Server:
SELECT
[dbo].[Machine].[MachineID],
[dbo].[Machine].[CompanyID],
[dbo].[Company].[AccountRef],
[dbo].[Machine].[ProductTypeID],
[dbo].[Machine].[SerialNo],
[dbo].[Machine].[InstallationDate],
[dbo].[Machine].[SalesTypeID],
[dbo].[SalesType].[SalesType],
[dbo].[Machine].[LeasingCompanyID],
[dbo].[LeasingCompany].[Name],
[dbo].[Machine].[QuarterlyRentalCost],
[dbo].[Machine].[Term],
[dbo].[Machine].[ExpiryDate],
[dbo].[Machine].[Scales],
[dbo].[Machine].[Chips],
[dbo].[Machine].[ContractTypeID],
[dbo].[ContractType].[ContractType],
[dbo].[Machine].[ContractCost],
[dbo].[Machine].[InvoiceDate],
[dbo].[Machine].[ServiceDueDate],
[dbo].[Machine].[ServiceNotes],
[dbo].[Machine].[modelID],
[dbo].[Machine].[Model],
[dbo].[Machine].[IMP_Machine Reference],
[dbo].[Machine].[Smart]
FROM
[dbo].[Machine], [dbo].[Company], [dbo].[SalesType], [dbo].[LeasingCompany], [dbo].[ContractType]
LEFT JOIN
[dbo].[Machine] as A ON A.[CompanyID] = [dbo].[Company].[CompanyID]
LEFT JOIN
[dbo].[Machine] as B ON B.[SalesTypeID] = [dbo].[SalesType].[SalesTypeID]
LEFT JOIN
[dbo].[Machine] as C ON C.[LeasingCompanyID] = [dbo].[LeasingCompany].[LeasingCompanyID]
LEFT JOIN
[dbo].[Machine] as D ON D.[ContractTypeID] = [dbo].[ContractType].[ContractTypeID] ;
But for some reason that i cannot see for the life of me, the destination column name in the bottom 3 join statements is reporting "The multi part identifier could not be bound".
Could anyone assist please?
Many Thanks,

Answer 1

You were pretty close, for readability, you dont need the extensive [dbo].[table] all over. You can define it once in the from clause with an alias, then use that alias the rest of the way through. Also, make the alias make sense to the context of the table as you will see in this below. LeasingCompany lc, SalesType st, etc.
Also, I try to have indented so I always know the first table of the join relationship and the JOIN indented on where it is being joined to. Then I keep the orientation of the from/to table aliases the same context.
Since the machine table is used once and joined to 4 different lookup tables, you can reuse the same "m" alias to each underlying. Think of a tree and branches. The root tree is your "Machine", and all the branches are the lookups.
SELECT
m.MachineID,
m.CompanyID,
c.AccountRef,
m.ProductTypeID,
m.SerialNo,
m.InstallationDate,
m.SalesTypeID,
st.SalesType,
m.LeasingCompanyID,
lc.LeasingCompany.Name,
m.QuarterlyRentalCost,
m.Term,
m.ExpiryDate,
m.Scales,
m.Chips,
m.ContractTypeID,
ct.ContractType,
m.ContractCost,
m.InvoiceDate,
m.ServiceDueDate,
m.ServiceNotes,
m.modelID,
m.Model,
m.IMP_Machine Reference,
m.Smart
FROM
Machine m
LEFT JOIN Company c
ON m.CompanyID = c.CompanyID
LEFT JOIN SalesType st
ON m.SalesTypeID = st.SalesTypeID
LEFT JOIN LeasingCompany lc
ON m.LeasingCompanyID = lc.LeasingCompanyID
LEFT JOIN ContractType ct
ON m.ContractTypeID = ct.ContractTypeID ;