T-SQL - Using Column Name in where condition without any references when having multiple tables that are engaged using multiple joins.

Question

Hi All,
I am a newbie for T-Sql, I came across a SP where multiple tables are engaged using multiple joins but the where clause contain  a column field without any table reference  and assigned  for an incoming variable,like 
where 'UserId = @UserId'
instead -  no table reference like 'a.UserId = @Userid'   ............ Can any please do refer to me any material that clears my mind regarding such issue................... help is appreciated.
Thank You.

Answer 1

As suggested above, use table alias with columns for unique referencing and to make the code easier to read.
BOL example for table aliasing:
USE AdventureWorks;
GO
SELECT S.CustomerID, S.Name AS Store, A.City, SP.Name AS State, CR.Name
AS CountryRegion
FROM Sales.Store AS S
JOIN Sales.CustomerAddress AS CA ON CA.CustomerID = S.CustomerID
JOIN Person.Address AS A ON A.AddressID = CA.AddressID
JOIN Person.StateProvince SP ON
SP.StateProvinceID = A.StateProvinceID
JOIN Person.CountryRegion CR ON
CR.CountryRegionCode = SP.CountryRegionCode
ORDER BY S.CustomerID ;
GO
GO
LINK:
http://technet.microsoft.com/en-us/library/ms124824(v=sql.100).aspx
Check the use of TABLE ALIASes and COLUMN ALIASes in the following blog:
http://www.sqlusa.com/bestpractices2005/organizationtree/
Without the use of aliases the code would become unreadable.
Kalman Toth Database & OLAP Architect
Free T-SQL Scripts
New Book / Kindle: Exam 70-461 Bootcamp: Querying Microsoft SQL Server 2012