Find the real column name of an alias used in a view? - sql

Question

Suppose I have a view in which some of the column names are aliases, like "surName" in this example:
CREATE VIEW myView AS
SELECT
firstName,
middleName,
you.lastName surName
FROM
myTable me
LEFT OUTER JOIN yourTable you
ON me.code = you.code
GO
I'm able to retrieve some information about the view using the INFORMATION_SCHEMA views.
For example, the query
SELECT column_name AS ALIAS, data_type AS TYPE
FROM information_schema.columns
WHERE table_name = 'myView'
yields:
----------------
|ALIAS |TYPE |
----------------
|firstName |nchar|
|middleName|nchar|
|surName |nchar|
----------------
However, I would like to know the actual column name as well. Ideally:
---------------------------
|ALIAS |TYPE |REALNAME |
---------------------------
|firstName |nchar|firstName |
|middleName|nchar|middleName|
|surName |nchar|lastName |
---------------------------
How can I determine what the real column name is based on the alias? There must be some way to use the sys tables and/or INFORMATION_SCHEMA views to retrieve this information.
EDIT:
I can get close with this abomination, which is similar to Arion's answer:
SELECT
c.name AS ALIAS,
ISNULL(type_name(c.system_type_id), t.name) AS DATA_TYPE,
tablecols.name AS REALNAME
FROM
sys.views v
JOIN sys.columns c ON c.object_id = v.object_id
LEFT JOIN sys.types t ON c.user_type_id = t.user_type_id
JOIN sys.sql_dependencies d ON d.object_id = v.object_id
AND c.column_id = d.referenced_minor_id
JOIN sys.columns tablecols ON d.referenced_major_id = tablecols.object_id
AND tablecols.column_id = d.referenced_minor_id
AND tablecols.column_id = c.column_id
WHERE v.name ='myView'
This yields:
---------------------------
|ALIAS |TYPE |REALNAME |
---------------------------
|firstName |nchar|firstName |
|middleName|nchar|middleName|
|surName |nchar|code |
|surName |nchar|lastName |
---------------------------
but the third record is wrong -- this happens with any view created using a "JOIN" clause, because there are two columns with the same "column_id", but in different tables.

Answer 1

Given this view:
CREATE VIEW viewTest
AS
SELECT
books.id,
books.author,
Books.title AS Name
FROM
Books
What I can see you can get the columns used and the tables used by doing this:
SELECT *
FROM INFORMATION_SCHEMA.VIEW_COLUMN_USAGE AS UsedColumns
WHERE UsedColumns.VIEW_NAME='viewTest'
SELECT *
FROM INFORMATION_SCHEMA.VIEW_TABLE_USAGE AS UsedTables
WHERE UsedTables.VIEW_NAME='viewTest'
This is for sql server 2005+. See reference here
Edit
Give the same view. Try this query:
SELECT
c.name AS columnName,
columnTypes.name as dataType,
aliases.name as alias
FROM
sys.views v
JOIN sys.sql_dependencies d
ON d.object_id = v.object_id
JOIN .sys.objects t
ON t.object_id = d.referenced_major_id
JOIN sys.columns c
ON c.object_id = d.referenced_major_id
JOIN sys.types AS columnTypes
ON c.user_type_id=columnTypes.user_type_id
AND c.column_id = d.referenced_minor_id
JOIN sys.columns AS aliases
on c.column_id=aliases.column_id
AND aliases.object_id = object_id('viewTest')
WHERE
v.name = 'viewTest';
It returns this for me:
columnName dataType alias
id int id
author varchar author
title varchar Name
This is also tested in sql 2005+

Answer 2

Having spent a number of hours trying to find an answer to this, and repeatedly running into solutions that didn't work and posters that appeared to eventually give up, I eventually stumbled across an answer here that appears to work:
https://social.msdn.microsoft.com/Forums/windowsserver/en-US/afa2ed2b-62de-4a5e-ae70-942e75f887a1/find-out-original-columns-name-when-used-in-a-view-with-alias?forum=transactsql
The following SQL returns, I believe, exactly what you're looking for, it's certainly doing what I need and appears to perform well too.
SELECT name
, source_database
, source_schema
, source_table
, source_column
, system_type_name
, is_identity_column
FROM sys.dm_exec_describe_first_result_set (N'SELECT * from ViewName', null, 1)
Documentation on the sys.dm_exec_describe_first_result_set function can be found here, it's available in SQL Server 2012 and later:
https://learn.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-exec-describe-first-result-set-transact-sql
Full credit to the poster on the link, I didn't work this out myself, but I wanted to post this here in case it's useful to anyone else searching for this information as I found this thread much more easily than the one I linked to.

Answer 3

I think you can't.
Select query hides actual data source it was performed against. Because you can query anything, i.e. view, table, even linked remote server.

Answer 4

Not a Perfect solution; but, it is possible to parse the view_definition with a high degree of accuracy especially if the code is well organized with consistent aliasing by 'as'. Additionally, one can parse for a comma ',' after the alias.
Of note: the final field in the select clause will not have the comma and I was unable to exclude items being used as comments (for example interlaced in the view text with --)
I wrote the below for a table named 'My_Table' and view correspondingly called 'vMy_Table'
select alias, t.COLUMN_name
from
(
select VC.COLUMN_NAME,
case when
ROW_NUMBER () OVER (
partition by C.COLUMN_NAME order by
CHARINDEX(',',VIEW_DEFINITION,CHARINDEX(C.COLUMN_NAME,VIEW_DEFINITION))-
CHARINDEX(VC.COLUMN_NAME,VIEW_DEFINITION)
) = 1
then 1
else 0 end
as lenDiff
,C.COLUMN_NAME as alias
,CHARINDEX(',',VIEW_DEFINITION,CHARINDEX(C.COLUMN_NAME,VIEW_DEFINITION)) diff1
, CHARINDEX(VC.COLUMN_NAME,VIEW_DEFINITION) diff2
from INFORMATION_SCHEMA.VIEW_COLUMN_USAGE VC
inner join INFORMATION_SCHEMA.VIEWS V on V.TABLE_NAME = 'v'+VC.TABLE_Name
inner join information_schema.COLUMNS C on C.TABLE_NAME = 'v'+VC.TABLE_Name
where VC.TABLE_NAME = 'My_Table'
and CHARINDEX(',',VIEW_DEFINITION,CHARINDEX(C.COLUMN_NAME,VIEW_DEFINITION))-
CHARINDEX(VC.COLUMN_NAME,VIEW_DEFINITION) >0
)
t
where lenDiff = 1
Hope this helps and I look forward to your feedback