T-SQL - Aliasing using "=" versus "as"

Question

Is there any particular reason (performance or otherwise) to use AS ahead of = when aliasing a column?

My personal preference (for readability) is to use this:

select
alias1     = somecolumn
alias2     = anothercolumn
from
tables
etc...

instead of this:

select
somecolumn as alias1
anothercolumn as alias2
from
tables
etc...

Am I missing out on any reason why I shouldn't be doing this? What are other people's preferences when it comes to formatting their columns?

Answer 1

I prefer using AS since = is used in the where statement, and can be confusing in a long query.

Answer 2

I wouldn't use it simply as it looks far too much like equality operation. 'AS' is clear inasmuch that it's not ambiguous to me.

Its the same as not using upper case in sql, I find it harder to read.

Answer 3

I prefer using neither of those. I just give the name of the column without any keyword in between

SELECT MAX(price_column) maximumprice FROM prices

Answer 4

**even i prefer using 'as' instead of '=' . '=' makes confusion in code.

e.g :

 column as alias1

Answer 5

To put in some counterweight, I prefer using =.

If I am the consumer of the query results in some way, I find it more convenient to see what columns I as a consumer can use.

I prefer this

SELECT
      [ElementObligationID] = @MaxElementObligationID + eo.ElementObligationID
      , [ElementID] = eo.ElementID
      , [IsotopeID] = eo.IsotopeID
      , [ObligationID] = eo.ObligationID
      , [ElementWeight] = eo.ElementWeight * -1
      , [FissileWeight] = eo.FissileWeight * -1
      , [Items] = eo.Items * -1
      , [Comment] = eo.Comment
      , [AdditionalComment] = eo.AdditionalComment
      , [Aanmaak_userid] = @UserID
      , [Aanmaak_tijdstip] = GetDate()
      , [Laatste_wijziging_userid] = @UserID
      , [Laatste_wijziging_tijdstip] = GetDate()
FROM  dbo.KTM_ElementObligation eo
      INNER JOIN dbo.KTM_ElementObligationArticle eoa ON 
          eoa.ElementObligationID = eo.ElementObligationID

over this

SELECT
      @MaxElementObligationID + eo.ElementObligationID AS [ElementObligationID]
      , eo.ElementID AS [ElementID]
      , eo.IsotopeID AS [IsotopeID]
      , eo.ObligationID AS [ObligationID]
      , eo.ElementWeight * -1 AS [ElementWeight]
      , eo.FissileWeight * -1 AS [FissileWeight]
      , eo.Items * -1 AS [Items]
      , eo.Comment AS [Comment]
      , eo.AdditionalComment AS [AdditionalComment]
      , @UserID AS [Aanmaak_userid]
      , GetDate() AS [Aanmaak_tijdstip]
      , @UserID AS [Laatste_wijziging_userid]
      , GetDate() AS [Laatste_wijziging_tijdstip]
FROM  dbo.KTM_ElementObligation eo
      INNER JOIN dbo.KTM_ElementObligationArticle eoa ON 
          eoa.ElementObligationID = eo.ElementObligationID

just my 2c.

Answer 6

= can be confused with assignment and equality; actually, the form I really don't like is when it looks like a string (usually when spaces are involved):

somecolumn as 'alias 1'

or

'alias 1' = somecolumn

I far prefer the alternative notation:

somecolumn as [alias 1]

Answer 7

"=" is just plain ambiguous.

If you indent to break out each select clause...

select
    alias1     = somecolumn,
    alias2     = anothercolumn,
    result     = column1 * column2
from
    table
....


select
    somecolumn as          alias1,
    anothercolumn as       alias2,
    column1 * column2 as   result
from
    tables
     ...

Answer 8

Column aliases declared by "=" syntax are deprecated in SQL Server 2008 and not supported in the next version. See MSDN article.

Answer 9

‘=’ isn't valid ANSI SQL, so you'll have difficulty should you wish to run your application on a different DBMS.

(It's when ANSI form is used but the optional ‘AS’ is omitted I find the results difficult to read, personally.)

Answer 10

The postfix alias form (with or without the "AS") is consistent between column and table aliases. Personally, I'd like an option to enforce the use of "AS", and then you wouldn't have the situation:

select
    columnA,
    columnB
    columnC
from
    table

producing a result set with two columns instead of the expected 3.

I'd also say that with the prefix "=" form, it can make it more difficult to read if you're mixing obtaining a result set and variable assignment:

select
    cA = columnA,
    @cB = columnB,
    cC = columnC
from
    table

Answer 11

While I have a preference for using AS, the really key thing here is to have a corporate standard and to follow it. If more of your people use AS than = then everyone should use it. Coding standards are what makes it easier to maintain code not the particular standard you pick. If everyone uses the same thing, then your eye gets used to picking it out.

Answer 12

The three ways I know of to alias:

1. TableColumn AS MyAlias
2. TableColumn MyAlias
3. MyAlias = TableColumn

Re: 1), I prefer this as it is the most self-documenting code (IMO), and it lets me search for AS if I need to find aliases..

Re: 2), This is my second choice, but without the AS, I am never sure whether this is a cut-and-paste error or not, especially in long, badly-formatted queries.

Re: 3), I don't like this because a) it looks like an assignment, and b) it blends in too much with ON clauses and CASE statements

So, my vote is to use the AS keyword for your aliases.

Answer 13

You don't have to use either

Drop the AS and use

SELECT originalname alias
FROM
   tablename

Answer 14

I like the

SELECT
 column1 = table.column1
 ,column2 = table.colum2
FROM table

I find AS not as easily noticable compared to a = sign (I can spot = quicker than AS)

Also when one just does SELECT column alias, sometimes it's confusing to know which one is which :)