Is it possible to assign a column to a variable in SQL Server?

[MdWebtress]

That is, in a stored procedure, I want to use 1 stored procedure to select from a table based on the result of any column the user chooses.

i.e.


declare @someColumn as nvarchar (don't know if there's another datatype for this)
declare @value as nvarchar
set @someColumn = someIDkey

select *
from myDB
where @someColumn = @value

Suppose I had a database that kept track of login info. I want to have 1 stored procedure instead of multiple ones that would only get info based on the userID, username, password, login time, etc.

In short, I'd like to combine these (hypothetically - not my actual database I'm using) into 1 stored procedure. Is it possible?

select *
from myDB
where userID = @value

select *
from myDB
where userName = @value

select *
from myDB
where loginTime = @value

select *
from myDB
where lastAction = @value

[russell]

Create Proc dbo.usp_myProc
  @col varchar(255),
  @value varchar(50)

AS

Exec('
  SELECT someFields
  FROM   myTable
  WHERE ' + @col + ' = ''' + @value + '''
)
GO

[russell]

as for the 2nd part of your question

Create Proc dbo.usp_myProc
  @userId int = null,
  @userName varchar(32) = null,
  @loginTime smalldatetime = null,
  @lastAction int = null

AS

Declare @sql varchar(1250)
Declare @where varchar(1250)
SET @sql = 'SELECT someFields FROM myTable '
SET @where = 'WHERE 1=1 '

IF @userId is NOT NULL
  SET @where = @where + 'AND userId = ' + cast(@userId as varchar(32)
IF @userName is NOT NULL
  SET @where = @where + ' AND userName = ''' + @userName + ''''

-- etc.
SET @sql = @sql + @where
Exec (@sql)

[russell]

You could also just execute SQL based on the condition:

IF @userName is NOT NULL
BEGIN
  SELECT * FROM myTable WHERE userNAme = @userName
  Return
END

IF @userId is NOT NULL
BEGIN
  SELECT * FROM myTable WHERE userId = @userId
  Return
END

That said, I'd still create several SPs. You'll get better performance, and you'll encapsulate good code that does one job well into it's own SP for easy re-use.