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Find last occurence of a character within a string
How to get a string from this string if it placed between slash , need to add functionality in this function
SELECT FieldA, COALESCE(RIGHT(FieldA, NULLIF(CHARINDEX('/', REVERSE(FieldA)) - 1, -1)), FieldA, '') AS FieldB
FROM (
  SELECT '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/' AS FieldA UNION ALL
  SELECT '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD' UNION ALL   
  SELECT NULL
) TableA

means for this string '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/'
or 
this string '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD'
or
this string '/index.cfm/fuseaction/content.page/nodeID/asdasd/'
UPD(Sorry): Not always this is GUID, and not always this is exactly content.page/nodeID - this is always some string between or start slash

search for nodeID and take the next however many characters?

For those people who love monster 1-liners. 
For MS2012 - Using IIF:
SELECT IIF(CHARINDEX('/', REVERSE(FieldA)) = 1,REVERSE(SUBSTRING(REVERSE(FieldA),2,CHARINDEX('/', SUBSTRING(REVERSE(FieldA), 2, LEN(FieldA))) - 1)),REVERSE(SUBSTRING(REVERSE(FieldA),1,CHARINDEX('/', REVERSE(FieldA)) - 1)))
FROM (
  SELECT '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/' AS FieldA 
  UNION ALL
  SELECT '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD' 
  UNION ALL   
  SELECT NULL
) TableA

For MS2008 Here is the same code in a CASE
SELECT A.FieldA
    ,   CASE 
            WHEN CHARINDEX('/', REVERSE(FieldA)) = 1 THEN REVERSE(SUBSTRING(REVERSE(FieldA),2,CHARINDEX('/', SUBSTRING(REVERSE(FieldA), 2, LEN(FieldA))) - 1)) 
            ELSE REVERSE(SUBSTRING(REVERSE(FieldA),1,CHARINDEX('/', REVERSE(FieldA)) - 1))
END
FROM (
  SELECT '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/' AS FieldA 
  UNION ALL
  SELECT '/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD' 
) a


how about without variables some like , IIF(CHARINDEX('/', REVERSE(FieldA)) > 1 ,RIGHT(FieldA, CHARINDEX('/', REVERSE(FieldA)) - 1) , CHARINDEX('/', SUBSTRING(REVERSE(FieldA),1,LEN(REVERSE(FieldA)))) ) as FieldB

@AleksP I've edited my answer to include the query as a single liner. Which appears to work... but I wouldn't like to maintain it!

Let us continue this discussion in chat.

This will find ANY GUID's in your data because it uses recursion to check each string in between two forward slashes
SELECT * INTO TableA
FROM
(
        SELECT 1 AS ID,'/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/' AS FieldA 
        UNION ALL
        SELECT 2,'/index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD' 
        --UNION ALL   
        --SELECT NULL
) tableA;

--CleanTableA makes sure that all values in FieldA end with a forward slash
WITH CleanTableA
AS
(
    SELECT  ID,
            CASE
                WHEN RIGHT(FieldA,1) = '/' THEN FieldA
                ELSE FieldA + '/'
            END FieldA
    FROM tableA
),
--Recursively finds the location of each forward slash
    --RecursionCount tells me if its the first,second,third,etc... forward slash
yourRecursiveCTE
AS
(
    SELECT ID,FieldA,CHARINDEX('/',FieldA,0) AS start, 1 AS recursionCount
    FROM CleanTableA
    UNION ALL
    SELECT CleanTableA.ID,CleanTableA.FieldA,CHARINDEX('/',CleanTableA.FieldA,CHARINDEX('/',CleanTableA.FieldA,yourRecursiveCTE.start) + 1) start,recursionCount + 1
    FROM CleanTableA
    INNER JOIN yourRecursiveCTE
    ON yourRecursiveCTE.ID = CleanTableA.ID
    WHERE CHARINDEX('/',CleanTableA.FieldA,CHARINDEX('/',CleanTableA.FieldA, yourRecursiveCTE.start) + 1) <> 0
)

SELECT  A.ID,
        A.FieldA,
        --Finds the gaps in between the "/"
        SUBSTRING(A.fieldA,A.start + 1,B.start-A.start - 1) possible_guid,
        --Tries to convert them to see if they are a GUID, if so then it returns the value
        TRY_CONVERT(uniqueidentifier,SUBSTRING(A.fieldA,A.start + 1,B.start-A.start - 1)) actual_guid
FROM yourRecursiveCTE A
INNER JOIN yourRecursiveCTE B
--Only compare the same values with same ID
ON A.ID = B.ID
--Join to forwards slash before it
AND A.recursionCount = B.recursionCount -1
--Uncomment where clause to only display GUID's
--WHERE TRY_CONVERT(uniqueidentifier,SUBSTRING(A.fieldA,A.start + 1,B.start-A.start - 1)) IS NOT NULL
ORDER BY A.ID,B.recursionCount

--Cleanup
DROP TABLE TableA

Results:
ID          FieldA                                                                           possible_guid                                                                    actual_guid
----------- -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- ------------------------------------
1           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  index.cfm                                                                        NULL
1           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  fuseaction                                                                       NULL
1           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  content.page                                                                     NULL
1           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  nodeID                                                                           NULL
1           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD                                             18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD
2           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  index.cfm                                                                        NULL
2           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  fuseaction                                                                       NULL
2           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  content.page                                                                     NULL
2           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  nodeID                                                                           NULL
2           /index.cfm/fuseaction/content.page/nodeID/18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD/  18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD                                             18156F6E-88E3-42FC-BDCB-DA6CBAD14EFD

