Reference an alias for an expression in a SELECT statement

Question

I have the following select statement that creates the expression "newdate" and then references in a different expression called "newname":

SELECT
Iif([DateColumn1]='',Format(CONVERT(DATE,Dateadd(day,RIGHT([DateColumn2],3)-1,CONVERT(DATETIME,LEFT([DateColumn2],4)))),'MMddyy'),Format(CONVERT(DATE,Dateadd(day,RIGHT(datecolumn3],3)-1,CONVERT(DATETIME,LEFT([DateColumn3],4)))),'MMddyy')) AS **newdate**,

Upper(LEFT(Rtrim([NameColumn4]),19)+''+[newdate]+''+RIGHT([NameColumn5],3)) AS newname

FROM   table1

For some reason when running this I get an error of invalid column and it refers to the "newdate" expression I created. The "newdate" expression works fine but it's when I add the second expression for "newname" that it stops working. Is there a way to refer to an expression as an alias within another expression that also has an alias?

Answer 1

You can't reference an alias within the same scope as its created - you can create it in a sub-query if you wish to avoid repeating the logic.

SELECT
    UPPER(LEFT(RTRIM([NameColumn4]),19)+''+[newdate]+''+RIGHT([NameColumn5],3)) AS [NewName]
FROM (
  SELECT NameColumn4, NameColumn5
      , IIF([DateColumn1]='',FORMAT(CONVERT(DATE,DATEADD(DAY,RIGHT([DateColumn2],3)-1,CONVERT(DATETIME,LEFT([DateColumn2],4)))),'MMddyy'),FORMAT(CONVERT(DATE,DATEADD(DAY,RIGHT(datecolumn3],3)-1,CONVERT(DATETIME,LEFT([DateColumn3],4)))),'MMddyy')) AS NewDate
  FROM table1
) X

Answer 2

You can't. But SQL Server has a very nifty feature where you can define the column in the from clause using apply :

SELECT v.newdate,
       Upper(LEFT(Rtrim(t1.[NameColumn4]),19) + v.newdate + RIGHT(t1.[NameColumn5], 3)) AS newname
FROM table1 t1 CROSS APPLY
     (VALUES ( <complicated expression here) 
     ) v(newdate)

Answer 3

In SQL Server, there is a concept called ALL AT ONCE, where all operations on a logical query execution phase (SELECT here).So, you are facing issue here.

Detailed Information on All at Once

SELECT FirstName + LastName AS FullName, 
       Salutation + FullName  -- Will throw error here
FROM TableName

You can handle that through multiple ways:

• Sub queries Dale K has suggested in another answer
• Common Table Expression Given below

;WITH CTE_NewDate AS
(
SELECT
Iif([DateColumn1]='',Format(CONVERT(DATE,Dateadd(day,RIGHT([DateColumn2],3)-1,CONVERT(DATETIME,LEFT([DateColumn2],4)))),'MMddyy'),Format(CONVERT(DATE,Dateadd(day,RIGHT(datecolumn3],3)-1,CONVERT(DATETIME,LEFT([DateColumn3],4)))),'MMddyy')) AS newdate,
NameColumn4, NameColumn5

FROM   table1
)
SELECT newDate, Upper(LEFT(Rtrim([NameColumn4]),19)+''+[newdate]+''+RIGHT([NameColumn5],3)) AS newname
FROM CTE_NewDate