How to use a created column as a JOIN parameter SQL query - sql

Question

I have 3 Tables of Data which i am trying to Join (TEXTDATA, STOREDATA, SALESDATA). My TEXTDATA has a name string within on of the columns so have created a substring to find it.
I am trying to then used that newly formed string (name) as the basis to join to the SALESDATA table.
Here is my code
SELECT b.*,
a.text,
a.textname,
SUBSTRING(a.[textname], CHARINDEX('/ ', a.[textname]) + 1, 11) AS NAME,
c.[Sales],
c.[Customer],
c.[Class]
FROM [dbo].[TEXTDATA] a
INNER JOIN [dbo].[STOREDATA] b
ON a.[ID_TEXTDATA] = b.[ID_STOREDATA]
LEFT JOIN [dbo].[SALESDATA] c
ON NAME = c.FirstName
With the error saying Invalid column name 'name'
Any ideas on how to reference the new column made later in a query?
Thanks very much!

Answer 1

Easiest option is just to use the same formula in the LEFT JOIN's ON clause:
LEFT JOIN [dbo].[SALESDATA] c
ON SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) = c.FirstName
Or you could put the formula in a CTE abstraction of your TEXTDATA table:
;with cte AS (
SELECT [ID_TEXTDATA], text, textname, SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) as name
From [dbo].[TEXTDATA] a
)
SELECT b.*
,cte.text
,cte.textname
,cte.name
,c.[Sales]
,c.[Customer]
,c.[Class]
From
cte
INNER JOIN [dbo].[STOREDATA] b
on cte.[ID_TEXTDATA] = b.[ID_STOREDATA]
LEFT JOIN [dbo].[SALESDATA] c
on cte.name = c.FirstName

Answer 2

Select b.*
,a.text
,a.textname
,SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) as name
,c.[Sales]
,c.[Customer]
,c.[Class]
From
[dbo].[TEXTDATA] a
INNER JOIN [dbo].[STOREDATA] b
on a.[ID_TEXTDATA] = b.[ID_STOREDATA]
LEFT JOIN [dbo].[SALESDATA] c
on SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) = c.FirstName
First, join takes place and can't find the name

Answer 3

I think you should try this in your ON CLAUSE:
SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11)
Select b.*,a.text,a.textname,SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11)
as name,c.[Sales] ,c.[Customer],c.[Class]
From [dbo].[TEXTDATA] a
INNER JOIN [dbo].[STOREDATA] b
on a.[ID_TEXTDATA] = b.[ID_STOREDATA]
LEFT JOIN [dbo].[SALESDATA] c
on SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) = c.FirstName

Answer 4

You can't reference the column alias name on the same level.
You have to use the entire expression on the ON
ON SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) = c.FirstName
Or you can make use of a CTE or derived query and compose the expression name in the CTE or derived query.
with Text_Data as
(
SELECT *,
SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) as [name]
FROM [dbo].[TEXTDATA] a
)
Select b.*
,a.text
,a.textname
,a.name
,c.[Sales]
,c.[Customer]
,c.[Class]
From
Text_Data a
INNER JOIN [dbo].[STOREDATA] b
on a.[ID_TEXTDATA] = b.[ID_STOREDATA]
LEFT JOIN [dbo].[SALESDATA] c
on a.name = c.FirstName
Or alternatively use a CROSS APPLY to compute the expression and then use it in the JOIN
Select b.*
,a.text
,a.textname
,n.name
,c.[Sales]
,c.[Customer]
,c.[Class]
From
[dbo].[TEXTDATA] a
CROSS APPLY
(
SELECT SUBSTRING(a.[textname],CHARINDEX('/ ',a.[textname])+1,11) as name
) n
INNER JOIN [dbo].[STOREDATA] b
on a.[ID_TEXTDATA] = b.[ID_STOREDATA]
LEFT JOIN [dbo].[SALESDATA] c
on n.name = c.FirstName

Answer 5

As the order of execution of SQL query says the select statement is run after all join statements so you can use alias in select for manipulation but not the same manipulated alias in join as join has already run by that time instead ypu need to have an extra select on top of it or using a WITH CLAUSE Subquery
Select *, name from ( select *,.. as
name from table) left join othertable
t1 on
name=t1.value
Or using WITH CLAUSE
WITH data as
( select *,.. as name from table)
Select * from data left join table1 t1
on data.name=t1.value