Question

I’m working with airline data, so I have a query like this

SELECT Invoices.PNR, Segments.Depart, Segments.Arrival, Segments.DepartDateTime
FROM Invoices AS i INNER JOIN Segments AS s
ON i.Invoice_ID = s.Invoice_ID`
WHERE PNR = 'AAAAAA'

This returns

PNR    Depart Arrival DepartDateTime
AAAAAA DFW    MCI     7/2/2012 7:30 AM
AAAAAA MCI    LAX     7/2/2012 11:30 AM
AAAAAA LAX    DFW     7/4/2012 2:30 PM

I have a column in Invoices called routing that I want to show ‘DFW-MCI-LAX-DFW’ Is this possible using a SQL only method ? The segments are listed in order, so DFW-MCI is first then MCI-LAX then LAX-DFW.

EDIT: If I could update the database with DFW-MCI-MCI-LAX-LAX-DFW that is perfectly acceptable. I can strip out the duplicate entries on the view layer.

I can easily write this in ColdFusion, but the looping and thousands of database updates takes forever. I could also do a mass update for every 100 records, but I’d like to avoid using anything other than SQL altogether

Answer 1

Here’s how you can update the values, assuming this is a one-time update (if it’s not, you’re going to have to run this every time Segments has any changes):

;WITH x AS 
(
  SELECT Invoice_ID, Routing = STUFF
  (
    (SELECT '-' + Depart + '-' + Arrival
      FROM dbo.Segments
      ORDER BY DepartDateTime
      FOR XML PATH(''), 
      TYPE).value(N'./text()[1]', N'varchar(max)'), 1, 1, '')
  FROM dbo.Segments
  GROUP BY Invoice_ID
)
UPDATE i SET Routing = x.Routing
  FROM dbo.Invoices AS i
  INNER JOIN x ON i.Invoice_ID = x.Invoice_ID;

Content of Invoices after the update:

PNR	Invoice_ID	Routing
AAAAAA	1	DFW-MCIMCI-LAXLAX-DFW

• Example db<>fiddle

If you are on SQL Server 2017 or greater, this is a lot easier with STRING_AGG():

;WITH cte(rt, id) AS
(
  SELECT STRING_AGG(CONCAT_WS('-', Depart, Arrival), '')
         WITHIN GROUP (ORDER BY DepartDateTime), Invoice_ID
  FROM dbo.Segments GROUP BY Invoice_ID
)
UPDATE i SET i.Routing = cte.rt
FROM dbo.Invoices AS i 
INNER JOIN cte ON i.Invoice_ID = cte.id;

• Example db<>fiddle