Optimizing a CTE hierarchy

Question

Update below

I have a table of accounts with a typical acct/parent account architecture to represent a hierarchy of accounts (SQL Server 2012). I created a VIEW using a CTE to hash out the hierarchy, and on the whole it works beautifully, and as intended. I can query the hierarchy at any level, and see the branches easily.

There is one business logic field that needs to be returned as a function of the hierarchy. A field in each account record describes the size of the business (we'll call it CustomerCount). The logic I need to report on needs to roll up the CustomerCount from the whole branch. In other words, given an account, I need to sum up the customercount values for that account along with every child in every branch below the account along the hierarchy.

I successfully calculated the field using a hierarchy field built within the CTE, which looks like acct4.acct3.acct2.acct1. The problem I'm running into is simply making it run fast. Without this one calculated field, the query runs in ~3 seconds. When I add in the calculated field, it turns into a 4 minute query.

Here is the best version I've been able to come up with that returns the correct results. I'm looking for ideas on how I can restructure this AS A VIEW without such huge sacrifices to performance.

I understand the reason this one goes slow (requires calculating a predicate in the where clause), but I can't think of another way to structure it and still get same results.

Here's some sample code to build a table and do the CTE pretty much exactly as it works in my environment.

Use Tempdb
go
CREATE TABLE dbo.Account
(
   Acctid varchar(1) NOT NULL
    , Name varchar(30) NULL
    , ParentId varchar(1) NULL
    , CustomerCount int NULL
);

INSERT Account
SELECT 'A','Best Bet',NULL,21  UNION ALL
SELECT 'B','eStore','A',30 UNION ALL
SELECT 'C','Big Bens','B',75 UNION ALL
SELECT 'D','Mr. Jimbo','B',50 UNION ALL
SELECT 'E','Dr. John','C',100 UNION ALL
SELECT 'F','Brick','A',222 UNION ALL
SELECT 'G','Mortar','C',153 ;


With AccountHierarchy AS

(                                                                           --Root values have no parent
    SELECT
        Root.AcctId                                         AccountId
        , Root.Name                                         AccountName
        , Root.ParentId                                     ParentId
        , 1                                                 HierarchyLevel  
        , cast(Root.Acctid as varchar(4000))                IdHierarchy     --highest parent reads right to left as in id3.Acctid2.Acctid1
        , cast(replace(Root.Name,'.','') as varchar(4000))  NameHierarchy   --highest parent reads right to left as in name3.name2.name1 (replace '.' so name parse is easy in last step)
        , cast(Root.Acctid as varchar(4000))                HierarchySort   --reverse of above, read left to right name1.name2.name3 for sorting on reporting only
        , cast(Root.Name as varchar(4000))                  HierarchyLabel  --use for labels on reporting only, indents names under sorted hierarchy
        , Root.CustomerCount                                CustomerCount   

    FROM 
        tempdb.dbo.account Root

    WHERE
        Root.ParentID is null

    UNION ALL

    SELECT
        Recurse.Acctid                                      AccountId
        , Recurse.Name                                      AccountName
        , Recurse.ParentId                                  ParentId
        , Root.HierarchyLevel + 1                           HierarchyLevel  --next level in hierarchy
        , cast(cast(recurse.Acctid as varchar(40)) + '.' + Root.IdHierarchy as varchar(4000))   IdHierarchy --cast because in real system this is a uniqueidentifier type needs converting
        , cast(replace(recurse.Name,'.','') + '.' + Root.NameHierarchy as varchar(4000)) NameHierarchy  --replace '.' for parsing in last step, cast to make room for lots of sub levels down the hierarchy
        , cast(Root.AccountName + '.' + Recurse.Name as varchar(4000)) HierarchySort    
        , cast(space(root.HierarchyLevel * 4) + Recurse.Name as varchar(4000)) HierarchyLabel
        , Recurse.CustomerCount                             CustomerCount

    FROM
        tempdb.dbo.account Recurse INNER JOIN
        AccountHierarchy Root on Root.AccountId = Recurse.ParentId
)


SELECT
    hier.AccountId
    , Hier.AccountName
    , hier.ParentId
    , hier.HierarchyLevel
    , hier.IdHierarchy
    , hier.NameHierarchy
    , hier.HierarchyLabel
    , parsename(hier.IdHierarchy,1) Acct1Id
    , parsename(hier.NameHierarchy,1) Acct1Name     --This is why we stripped out '.' during recursion
    , parsename(hier.IdHierarchy,2) Acct2Id
    , parsename(hier.NameHierarchy,2) Acct2Name
    , parsename(hier.IdHierarchy,3) Acct3Id
    , parsename(hier.NameHierarchy,3) Acct3Name
    , parsename(hier.IdHierarchy,4) Acct4Id
    , parsename(hier.NameHierarchy,4) Acct4Name
    , hier.CustomerCount

    /* fantastic up to this point. Next block of code is what causes problem. 
        Logic of code is "sum of CustomerCount for this location and all branches below in this branch of hierarchy"
        In live environment, goes from taking 3 seconds to 4 minutes by adding this one calc */

    , (
        SELECT  
            sum(children.CustomerCount)
        FROM
            AccountHierarchy Children
        WHERE
            hier.IdHierarchy = right(children.IdHierarchy, (1 /*length of id field*/ * hier.HierarchyLevel) + hier.HierarchyLevel - 1 /*for periods inbetween ids*/)
            --"where this location's idhierarchy is within child idhierarchy"
            --previously tried a charindex(hier.IdHierarchy,children.IdHierarchy)>0, but that performed even worse
        ) TotalCustomerCount
FROM
    AccountHierarchy hier

ORDER BY
    hier.HierarchySort


drop table tempdb.dbo.Account

11/20/2013 UPDATE

Some of the suggested solutions got my juices flowing, and I tried a new approach that comes close, but introduces a new/different obstacle. Honestly, I don't know if this warrants a separate post or not, but it's related to the solution of this problem.

What I decided was that what was making the sum(customercount) difficult is the identification of children in the context of a hierarchy that starts at the top and builds down. So I started by creating a hierarchy that builds from the bottom up, using the root defined by "accounts that are not parent to any other account" and doing the recursive join backwards (root.parentacctid = recurse.acctid)

This way I could just add the child customer count to the parent as the recursion happens. Because of how I need reporting, and levels, I am doing this bottom up cte in addition to the top down, then just joining them via account id. This approach turns out to be much faster than the original outer query customercount, but I ran into a few obstacles.

First, I was inadvertently capturing duplicative customer count for accounts that are parent to multiple children. I was double or triple counting customer count for some acctid's, by the number of children there were. My solution was to create yet another cte which counts how many nodes an acct has, and divide the acct.customercount during recursion, so when I add up the whole branch the acct is not being double counted.

So at this point, the results of this new version are not correct, but I know why. The bottomup cte is creating duplicates. When the recursion passes, it looks for anything in the root (bottom level children) that is child to an account in the account table. On the third recursion, it picks up the same accounts it did in the second and puts them in again.

Ideas on how to do a bottom up cte, or does this get any other ideas flowing?

Use Tempdb
go


CREATE TABLE dbo.Account
(
    Acctid varchar(1) NOT NULL
    , Name varchar(30) NULL
    , ParentId varchar(1) NULL
    , CustomerCount int NULL
);

INSERT Account
SELECT 'A','Best Bet',NULL,1  UNION ALL
SELECT 'B','eStore','A',2 UNION ALL
SELECT 'C','Big Bens','B',3 UNION ALL
SELECT 'D','Mr. Jimbo','B',4 UNION ALL
SELECT 'E','Dr. John','C',5 UNION ALL
SELECT 'F','Brick','A',6 UNION ALL
SELECT 'G','Mortar','C',7 ;



With AccountHierarchy AS

(                                                                           --Root values have no parent
    SELECT
        Root.AcctId                                         AccountId
        , Root.Name                                         AccountName
        , Root.ParentId                                     ParentId
        , 1                                                 HierarchyLevel  
        , cast(Root.Acctid as varchar(4000))                IdHierarchy     --highest parent reads right to left as in id3.Acctid2.Acctid1
        , cast(replace(Root.Name,'.','') as varchar(4000))  NameHierarchy   --highest parent reads right to left as in name3.name2.name1 (replace '.' so name parse is easy in last step)
        , cast(Root.Acctid as varchar(4000))                HierarchySort   --reverse of above, read left to right name1.name2.name3 for sorting on reporting only
        , cast(Root.Acctid as varchar(4000))                HierarchyMatch 
        , cast(Root.Name as varchar(4000))                  HierarchyLabel  --use for labels on reporting only, indents names under sorted hierarchy
        , Root.CustomerCount                                CustomerCount   

    FROM 
        tempdb.dbo.account Root

    WHERE
        Root.ParentID is null

    UNION ALL

    SELECT
        Recurse.Acctid                                      AccountId
        , Recurse.Name                                      AccountName
        , Recurse.ParentId                                  ParentId
        , Root.HierarchyLevel + 1                           HierarchyLevel  --next level in hierarchy
        , cast(cast(recurse.Acctid as varchar(40)) + '.' + Root.IdHierarchy as varchar(4000))   IdHierarchy --cast because in real system this is a uniqueidentifier type needs converting
        , cast(replace(recurse.Name,'.','') + '.' + Root.NameHierarchy as varchar(4000)) NameHierarchy  --replace '.' for parsing in last step, cast to make room for lots of sub levels down the hierarchy
        , cast(Root.AccountName + '.' + Recurse.Name as varchar(4000)) HierarchySort    
        , CAST(CAST(Root.HierarchyMatch as varchar(40)) + '.' 
            + cast(recurse.Acctid as varchar(40))   as varchar(4000))   HierarchyMatch
        , cast(space(root.HierarchyLevel * 4) + Recurse.Name as varchar(4000)) HierarchyLabel
        , Recurse.CustomerCount                             CustomerCount

    FROM
        tempdb.dbo.account Recurse INNER JOIN
        AccountHierarchy Root on Root.AccountId = Recurse.ParentId
)

, Nodes as
(   --counts how many branches are below for any account that is parent to another
    select
        node.ParentId Acctid
        , cast(count(1) as float) Nodes
    from AccountHierarchy  node
    group by ParentId
)

, BottomUp as
(   --creates the hierarchy starting at accounts that are not parent to any other
    select
        Root.Acctid
        , root.ParentId
        , cast(isnull(root.customercount,0) as float) CustomerCount
    from
        tempdb.dbo.Account Root
    where
        not exists ( select 1 from tempdb.dbo.Account OtherAccts where root.Acctid = OtherAccts.ParentId)

    union all

    select
        Recurse.Acctid
        , Recurse.ParentId
        , root.CustomerCount + cast ((isnull(recurse.customercount,0) / nodes.nodes) as float) CustomerCount
        -- divide the recurse customercount by number of nodes to prevent duplicate customer count on accts that are parent to multiple children, see customercount cte next
    from
        tempdb.dbo.Account Recurse inner join 
        BottomUp Root on root.ParentId = recurse.acctid inner join
        Nodes on nodes.Acctid = recurse.Acctid
)

, CustomerCount as
(
    select
        sum(CustomerCount) TotalCustomerCount
        , hier.acctid
    from
        BottomUp hier
    group by 
        hier.Acctid
)


SELECT
    hier.AccountId
    , Hier.AccountName
    , hier.ParentId
    , hier.HierarchyLevel
    , hier.IdHierarchy
    , hier.NameHierarchy
    , hier.HierarchyLabel
    , hier.hierarchymatch
    , parsename(hier.IdHierarchy,1) Acct1Id
    , parsename(hier.NameHierarchy,1) Acct1Name     --This is why we stripped out '.' during recursion
    , parsename(hier.IdHierarchy,2) Acct2Id
    , parsename(hier.NameHierarchy,2) Acct2Name
    , parsename(hier.IdHierarchy,3) Acct3Id
    , parsename(hier.NameHierarchy,3) Acct3Name
    , parsename(hier.IdHierarchy,4) Acct4Id
    , parsename(hier.NameHierarchy,4) Acct4Name
    , hier.CustomerCount

    , customercount.TotalCustomerCount

FROM
    AccountHierarchy hier inner join
    CustomerCount on customercount.acctid = hier.accountid

ORDER BY
    hier.HierarchySort 



drop table tempdb.dbo.Account

Answer 1

Edit: this is second attempt

Based on @Hannah Vernon's answer, here is a way to bypass the use of CTE inside an inline subquery, which is like self-joining the CTE and I presume is the reason for the poor efficiency. It uses analytic functions available only in the 2012 version of SQL-Server. Tested at SQL-Fiddle

This part can be skipped from reading, it's a copy-paste from Hannah's answer:

;With AccountHierarchy AS
(                                                                           
    SELECT
        Root.AcctId                                         AccountId
        , Root.Name                                         AccountName
        , Root.ParentId                                     ParentId
        , 1                                                 HierarchyLevel  
        , cast(Root.Acctid as varchar(4000))                IdHierarchyMatch        
        , cast(Root.Acctid as varchar(4000))                IdHierarchy
        , cast(replace(Root.Name,'.','') as varchar(4000))  NameHierarchy   
        , cast(Root.Acctid as varchar(4000))                HierarchySort
        , cast(Root.Name as varchar(4000))                  HierarchyLabel          ,
        Root.CustomerCount                                  CustomerCount   

    FROM 
        account Root

    WHERE
        Root.ParentID is null

    UNION ALL

    SELECT
        Recurse.Acctid                                      AccountId
        , Recurse.Name                                      AccountName
        , Recurse.ParentId                                  ParentId
        , Root.HierarchyLevel + 1                           HierarchyLevel
        , CAST(CAST(Root.IdHierarchyMatch as varchar(40)) + '.' 
            + cast(recurse.Acctid as varchar(40))   as varchar(4000))   IdHierarchyMatch
        , cast(cast(recurse.Acctid as varchar(40)) + '.' 
            + Root.IdHierarchy  as varchar(4000))           IdHierarchy
        , cast(replace(recurse.Name,'.','') + '.' 
            + Root.NameHierarchy as varchar(4000))          NameHierarchy
        , cast(Root.AccountName + '.' 
            + Recurse.Name as varchar(4000))                HierarchySort   
        , cast(space(root.HierarchyLevel * 4) 
            + Recurse.Name as varchar(4000))                HierarchyLabel
        , Recurse.CustomerCount                             CustomerCount
    FROM
        account Recurse INNER JOIN
        AccountHierarchy Root on Root.AccountId = Recurse.ParentId
)

Here we order the rows of the CTE using the IdHierarchyMatch and we calculate row numbers and a running total (from the next row up to the end.)

, cte1 AS 
(
SELECT
    h.AccountId
    , h.AccountName
    , h.ParentId
    , h.HierarchyLevel
    , h.IdHierarchy
    , h.NameHierarchy
    , h.HierarchyLabel
    , parsename(h.IdHierarchy,1) Acct1Id
    , parsename(h.NameHierarchy,1) Acct1Name
    , parsename(h.IdHierarchy,2) Acct2Id
    , parsename(h.NameHierarchy,2) Acct2Name
    , parsename(h.IdHierarchy,3) Acct3Id
    , parsename(h.NameHierarchy,3) Acct3Name
    , parsename(h.IdHierarchy,4) Acct4Id
    , parsename(h.NameHierarchy,4) Acct4Name
    , h.CustomerCount
    , h.HierarchySort
    , h.IdHierarchyMatch
        , Rn = ROW_NUMBER() OVER 
                  (ORDER BY h.IdHierarchyMatch)
        , RunningCustomerCount = COALESCE(
            SUM(h.CustomerCount)
            OVER
              (ORDER BY h.IdHierarchyMatch
               ROWS BETWEEN 1 FOLLOWING
                        AND UNBOUNDED FOLLOWING)
          , 0) 
FROM
    AccountHierarchy AS h  
)

Then we have one more intermediate CTE where we use the previous running totals and row numbers - basically to find where the end points for the branches of the tree structure:

, cte2 AS
(
SELECT
    cte1.*
    , rn3  = LAST_VALUE(Rn) OVER 
               (PARTITION BY Acct1Id, Acct2Id, Acct3Id 
                ORDER BY Acct4Id
                ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)       
    , rn2  = LAST_VALUE(Rn) OVER 
               (PARTITION BY Acct1Id, Acct2Id 
                ORDER BY Acct3Id, Acct4Id
                ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) 
    , rn1  = LAST_VALUE(Rn) OVER 
               (PARTITION BY Acct1Id 
                ORDER BY Acct2Id, Acct3Id, Acct4Id
                ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) 
    , rcc3 = LAST_VALUE(RunningCustomerCount) OVER 
               (PARTITION BY Acct1Id, Acct2Id, Acct3Id 
                ORDER BY Acct4Id
                ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)       
    , rcc2 = LAST_VALUE(RunningCustomerCount) OVER 
               (PARTITION BY Acct1Id, Acct2Id 
                ORDER BY Acct3Id, Acct4Id
                ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) 
    , rcc1 = LAST_VALUE(RunningCustomerCount) OVER 
               (PARTITION BY Acct1Id 
                ORDER BY Acct2Id, Acct3Id, Acct4Id
                ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) 
FROM
    cte1 
) 

and finally we build the last part:

SELECT
    hier.AccountId
    , hier.AccountName
    ---                        -- columns skipped 
    , hier.CustomerCount

    , TotalCustomerCount = hier.CustomerCount
        + hier.RunningCustomerCount 
        - ca.LastRunningCustomerCount

    , hier.HierarchySort
    , hier.IdHierarchyMatch
FROM
    cte2 hier
  OUTER APPLY
    ( SELECT  LastRunningCustomerCount, Rn
      FROM
      ( SELECT LastRunningCustomerCount
              = RunningCustomerCount, Rn
        FROM (SELECT NULL a) x  WHERE 4 <= HierarchyLevel 
      UNION ALL
        SELECT rcc3, Rn3
        FROM (SELECT NULL a) x  WHERE 3 <= HierarchyLevel 
      UNION ALL
        SELECT rcc2, Rn2 
        FROM (SELECT NULL a) x  WHERE 2 <= HierarchyLevel 
      UNION ALL
        SELECT rcc1, Rn1
        FROM (SELECT NULL a) x  WHERE 1 <= HierarchyLevel 
      ) x
      ORDER BY Rn 
      OFFSET 0 ROWS
      FETCH NEXT 1 ROWS ONLY
      ) ca
ORDER BY
    hier.HierarchySort ; 

---

And a simplification, using the same cte1 as the code above. Test at SQL-Fiddle-2. Please note that both solutions work under the assumption that you have a maximum of four levels in your tree:

SELECT
    hier.AccountId
    ---                      -- skipping rows
    , hier.CustomerCount

    , TotalCustomerCount = CustomerCount
        + RunningCustomerCount 
        - CASE HierarchyLevel
            WHEN 4 THEN RunningCustomerCount
            WHEN 3 THEN LAST_VALUE(RunningCustomerCount) OVER 
                   (PARTITION BY Acct1Id, Acct2Id, Acct3Id 
                    ORDER BY Acct4Id
                    ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)       
            WHEN 2 THEN LAST_VALUE(RunningCustomerCount) OVER 
                   (PARTITION BY Acct1Id, Acct2Id 
                    ORDER BY Acct3Id, Acct4Id
                    ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) 
            WHEN 1 THEN LAST_VALUE(RunningCustomerCount) OVER 
                   (PARTITION BY Acct1Id 
                    ORDER BY Acct2Id, Acct3Id, Acct4Id
                    ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) 
          END

    , hier.HierarchySort
    , hier.IdHierarchyMatch
FROM cte1 AS hier
ORDER BY
    hier.HierarchySort ; 

---

A third approach, with only one CTE, for the recursive part and then only window aggregate functions (SUM() OVER (...)), so it should work in any version from 2005 upwards. Test at SQL-Fiddle-3 This solution assumes, like the previous ones, that there are 4 levels maximum in the hierarchy tree:

;WITH AccountHierarchy AS
(                                                                           
    SELECT
          AccountId      = Root.AcctId                                         
        , AccountName    = Root.Name                                         
        , ParentId       = Root.ParentId                                     
        , HierarchyLevel = 1                                                   
        , HierarchySort  = CAST(Root.Acctid AS VARCHAR(4000))                
        , HierarchyLabel = CAST(Root.Name AS VARCHAR(4000))                   
        , Acct1Id        = CAST(Root.Acctid AS VARCHAR(4000))                
        , Acct2Id        = CAST(NULL AS VARCHAR(4000))                       
        , Acct3Id        = CAST(NULL AS VARCHAR(4000))                       
        , Acct4Id        = CAST(NULL AS VARCHAR(4000))                       
        , Acct1Name      = CAST(Root.Name AS VARCHAR(4000))                  
        , Acct2Name      = CAST(NULL AS VARCHAR(4000))                       
        , Acct3Name      = CAST(NULL AS VARCHAR(4000))                       
        , Acct4Name      = CAST(NULL AS VARCHAR(4000))                       
        , CustomerCount  = Root.CustomerCount                                   

    FROM 
        account AS Root

    WHERE
        Root.ParentID IS NULL

    UNION ALL

    SELECT
          Recurse.Acctid 
        , Recurse.Name 
        , Recurse.ParentId 
        , Root.HierarchyLevel + 1 
        , CAST(Root.AccountName + '.' 
            + Recurse.Name AS VARCHAR(4000)) 
        , CAST(SPACE(Root.HierarchyLevel * 4) 
            + Recurse.Name AS VARCHAR(4000)) 
        , Root.Acct1Id 
        , CASE WHEN Root.HierarchyLevel = 1 
              THEN cast(Recurse.Acctid AS VARCHAR(4000)) 
              ELSE Root.Acct2Id 
          END 
        , CASE WHEN Root.HierarchyLevel = 2 
              THEN CAST(Recurse.Acctid AS VARCHAR(4000)) 
              ELSE Root.Acct3Id 
          END 
        , CASE WHEN Root.HierarchyLevel = 3 
              THEN CAST(Recurse.Acctid AS VARCHAR(4000)) 
              ELSE Root.Acct4Id 
          END 
 
        , cast(Root.AccountName as varchar(4000))          
        , CASE WHEN Root.HierarchyLevel = 1 
              THEN CAST(Recurse.Name AS VARCHAR(4000)) 
              ELSE Root.Acct2Name 
          END 
        , CASE WHEN Root.HierarchyLevel = 2 
              THEN CAST(Recurse.Name AS VARCHAR(4000)) 
              ELSE Root.Acct3Name 
          END 
        , CASE WHEN Root.HierarchyLevel = 3 
              THEN CAST(Recurse.Name AS VARCHAR(4000)) 
              ELSE Root.Acct4Name 
          END 
        , Recurse.CustomerCount 
    FROM 
        account AS Recurse INNER JOIN 
        AccountHierarchy AS Root ON Root.AccountId = Recurse.ParentId
)

SELECT
      h.AccountId
    , h.AccountName
    , h.ParentId
    , h.HierarchyLevel
    , IdHierarchy = 
          CAST(COALESCE(h.Acct4Id+'.','') 
               + COALESCE(h.Acct3Id+'.','') 
               + COALESCE(h.Acct2Id+'.','') 
               + h.Acct1Id AS VARCHAR(4000))
    , NameHierarchy = 
          CAST(COALESCE(h.Acct4Name+'.','') 
               + COALESCE(h.Acct3Name+'.','') 
               + COALESCE(h.Acct2Name+'.','') 
               + h.Acct1Name AS VARCHAR(4000))   
    , h.HierarchyLabel
    , h.Acct1Id
    , h.Acct1Name
    , h.Acct2Id
    , h.Acct2Name
    , h.Acct3Id
    , h.Acct3Name
    , h.Acct4Id
    , h.Acct4Name
    , h.CustomerCount
    , TotalCustomerCount =  
          CASE h.HierarchyLevel
            WHEN 4 THEN h.CustomerCount
            WHEN 3 THEN SUM(h.CustomerCount) OVER 
                   (PARTITION BY h.Acct1Id, h.Acct2Id, h.Acct3Id)       
            WHEN 2 THEN SUM(h.CustomerCount) OVER 
                   (PARTITION BY Acct1Id, h.Acct2Id) 
            WHEN 1 THEN SUM(h.CustomerCount) OVER 
                   (PARTITION BY h.Acct1Id) 
          END
    , h.HierarchySort
    , IdHierarchyMatch = 
          CAST(h.Acct1Id 
               + COALESCE('.'+h.Acct2Id,'') 
               + COALESCE('.'+h.Acct3Id,'') 
               + COALESCE('.'+h.Acct4Id,'') AS VARCHAR(4000))   
FROM
    AccountHierarchy AS h  
ORDER BY
    h.HierarchySort ; 

---

A 4th approach, that calculates as an intermediate CTE, the closure table of the hierarchy. Test at SQL-Fiddle-4. The benefit is that for the sums calculations, there is no resctriction on the number of levels.

;WITH AccountHierarchy AS
( 
    -- skipping several line, identical to the 3rd approach above
)

, ClosureTable AS
( 
    SELECT
          AccountId      = Root.AcctId  
        , AncestorId     = Root.AcctId  
        , CustomerCount  = Root.CustomerCount 
    FROM 
        account AS Root

    UNION ALL

    SELECT
          Recurse.Acctid 
        , Root.AncestorId 
        , Recurse.CustomerCount
    FROM 
        account AS Recurse INNER JOIN 
        ClosureTable AS Root ON Root.AccountId = Recurse.ParentId
)

, ClosureGroup AS
(                                                                           
    SELECT
          AccountId           = AncestorId  
        , TotalCustomerCount  = SUM(CustomerCount)                             
    FROM 
        ClosureTable AS a
    GROUP BY
        AncestorId
)

SELECT
      h.AccountId
    , h.AccountName
    , h.ParentId
    , h.HierarchyLevel 
    , h.HierarchyLabel
    , h.CustomerCount
    , cg.TotalCustomerCount 

    , h.HierarchySort
FROM
    AccountHierarchy AS h  
  JOIN
    ClosureGroup AS cg
      ON cg.AccountId = h.AccountId
ORDER BY
    h.HierarchySort ;  

Answer 2

I believe this should make it faster:

;With AccountHierarchy AS
(                                                                           
    SELECT
        Root.AcctId                                         AccountId
        , Root.Name                                         AccountName
        , Root.ParentId                                     ParentId
        , 1                                                 HierarchyLevel  
        , cast(Root.Acctid as varchar(4000))                IdHierarchyMatch        
        , cast(Root.Acctid as varchar(4000))                IdHierarchy
        , cast(replace(Root.Name,'.','') as varchar(4000))  NameHierarchy   
        , cast(Root.Acctid as varchar(4000))                HierarchySort
        , cast(Root.Name as varchar(4000))                  HierarchyLabel          ,
        Root.CustomerCount                                  CustomerCount   

    FROM 
        tempdb.dbo.account Root

    WHERE
        Root.ParentID is null

    UNION ALL

    SELECT
        Recurse.Acctid                                      AccountId
        , Recurse.Name                                      AccountName
        , Recurse.ParentId                                  ParentId
        , Root.HierarchyLevel + 1                           HierarchyLevel
        , CAST(CAST(Root.IdHierarchyMatch as varchar(40)) + '.' 
            + cast(recurse.Acctid as varchar(40))   as varchar(4000))   IdHierarchyMatch
        , cast(cast(recurse.Acctid as varchar(40)) + '.' 
            + Root.IdHierarchy  as varchar(4000))           IdHierarchy
        , cast(replace(recurse.Name,'.','') + '.' 
            + Root.NameHierarchy as varchar(4000))          NameHierarchy
        , cast(Root.AccountName + '.' 
            + Recurse.Name as varchar(4000))                HierarchySort   
        , cast(space(root.HierarchyLevel * 4) 
            + Recurse.Name as varchar(4000))                HierarchyLabel
        , Recurse.CustomerCount                             CustomerCount
    FROM
        tempdb.dbo.account Recurse INNER JOIN
        AccountHierarchy Root on Root.AccountId = Recurse.ParentId
)


SELECT
    hier.AccountId
    , Hier.AccountName
    , hier.ParentId
    , hier.HierarchyLevel
    , hier.IdHierarchy
    , hier.NameHierarchy
    , hier.HierarchyLabel
    , parsename(hier.IdHierarchy,1) Acct1Id
    , parsename(hier.NameHierarchy,1) Acct1Name
    , parsename(hier.IdHierarchy,2) Acct2Id
    , parsename(hier.NameHierarchy,2) Acct2Name
    , parsename(hier.IdHierarchy,3) Acct3Id
    , parsename(hier.NameHierarchy,3) Acct3Name
    , parsename(hier.IdHierarchy,4) Acct4Id
    , parsename(hier.NameHierarchy,4) Acct4Name
    , hier.CustomerCount
    , (
        SELECT  
            sum(children.CustomerCount)
        FROM
            AccountHierarchy Children
        WHERE
            Children.IdHierarchyMatch LIKE hier.IdHierarchyMatch + '%'
        ) TotalCustomerCount
        , HierarchySort
        , IdHierarchyMatch
FROM
    AccountHierarchy hier
ORDER BY
    hier.HierarchySort

I added a column in the CTE named IdHierarchyMatch which is the forward version of IdHierarchy to enable the TotalCustomerCount subquery WHERE clause to be sargable.

Comparing estimated subtree costs for the execution plans, this way should be approximately 5 times faster.

Answer 3

I gave it a shot as well. It ain't very pretty, but it seems to perform better.

USE Tempdb
go

SET STATISTICS IO ON;
SET STATISTICS TIME OFF;
SET NOCOUNT ON;

--------
-- assuming the original table looks something like this 
-- and you cannot control it's indexes 
-- (only widened the data types a bit for the extra sample rows)
--------
CREATE TABLE dbo.Account
    (
      Acctid VARCHAR(10) NOT NULL ,
      Name VARCHAR(100) NULL ,
      ParentId VARCHAR(10) NULL ,
      CustomerCount INT NULL
    );

--------
-- inserting the same records as in your sample
--------
INSERT  Account
        SELECT  'A' ,
                'Best Bet' ,
                NULL ,
                21
        UNION ALL
        SELECT  'B' ,
                'eStore' ,
                'A' ,
                30
        UNION ALL
        SELECT  'C' ,
                'Big Bens' ,
                'B' ,
                75
        UNION ALL
        SELECT  'D' ,
                'Mr. Jimbo' ,
                'B' ,
                50
        UNION ALL
        SELECT  'E' ,
                'Dr. John' ,
                'C' ,
                100
        UNION ALL
        SELECT  'F' ,
                'Brick' ,
                'A' ,
                222
        UNION ALL
        SELECT  'G' ,
                'Mortar' ,
                'C' ,
                153;

--------
-- now lets up the ante a bit and add some extra rows with random parents 
-- to these 7 items, it is hard to measure differences with so few rows
--------
DECLARE @numberOfRows INT = 25000
DECLARE @from INT = 1
DECLARE @to INT = 7
DECLARE @T1 TABLE ( n INT ); 

WITH    cte ( n )
          AS ( SELECT   ROW_NUMBER() OVER ( ORDER BY CURRENT_TIMESTAMP )
               FROM     sys.messages
             )
    INSERT  INTO @T1
            SELECT  n
            FROM    cte
            WHERE   n <= @numberOfRows;

INSERT  INTO dbo.Account
        ( acctId ,
          name ,
          parentId ,
          Customercount
        )
        SELECT  CHAR(64 + RandomNumber) + CAST(n AS VARCHAR(10)) AS Id ,
                CAST('item ' + CHAR(64 + RandomNumber) + CAST(n AS VARCHAR(10)) AS VARCHAR(100)) ,
                CHAR(64 + RandomNumber) AS parentId ,
                ABS(CHECKSUM(NEWID()) % 100) + 1 AS RandomCustCount
        FROM    ( SELECT    n ,
                            ABS(CHECKSUM(NEWID()) % @to) + @from AS RandomNumber
                  FROM      @T1
                ) A;

--------
-- Assuming you cannot control it's indexes, in my tests we're better off taking the IO hit of copying the data
-- to some structure that is better optimized for this query. Not quite what I initially expected,  but we seem 
-- to be better off that way.
--------
CREATE TABLE tempdb.dbo.T1
    (
      AccountId VARCHAR(10) NOT NULL
                            PRIMARY KEY NONCLUSTERED ,
      AccountName VARCHAR(100) NOT NULL ,
      ParentId VARCHAR(10) NULL ,
      HierarchyLevel INT NULL ,
      HPath VARCHAR(1000) NULL ,
      IdHierarchy VARCHAR(1000) NULL ,
      NameHierarchy VARCHAR(1000) NULL ,
      HierarchyLabel VARCHAR(1000) NULL ,
      HierarchySort VARCHAR(1000) NULL ,
      CustomerCount INT NOT NULL
    );

CREATE CLUSTERED INDEX IX_Q1
ON tempdb.dbo.T1  ([ParentId]);

-- for summing customer counts over parents
CREATE NONCLUSTERED INDEX IX_Q2 
ON tempdb.dbo.T1  (HPath) INCLUDE(CustomerCount);

INSERT  INTO tempdb.dbo.T1
        ( AccountId ,
          AccountName ,
          ParentId ,
          HierarchyLevel ,
          HPath ,
          IdHierarchy ,
          NameHierarchy ,
          HierarchyLabel ,
          HierarchySort ,
          CustomerCount 
        )
        SELECT  Acctid AS AccountId ,
                Name AS AccountName ,
                ParentId AS ParentId ,
                NULL AS HierarchyLevel ,
                NULL AS HPath ,
                NULL AS IdHierarchy ,
                NULL AS NameHierarchy ,
                NULL AS HierarchyLabel ,
                NULL AS HierarchySort ,
                CustomerCount AS CustomerCount
        FROM    tempdb.dbo.account;



--------
-- I cannot seem to force an efficient way to do the sum while selecting over the recursive cte, 
-- so I took it aside. I am sure there is a more elegant way but I can't seem to make it happen. 
-- At least it performs better this way. But it remains a very expensive query.
--------
;
WITH    AccountHierarchy
          AS ( SELECT   Root.AccountId AS AcId ,
                        Root.ParentId ,
                        1 AS HLvl ,
                        CAST(Root.AccountId AS VARCHAR(1000)) AS [HPa] ,
                        CAST(Root.accountId AS VARCHAR(1000)) AS hid ,
                        CAST(REPLACE(Root.AccountName, '.', '') AS VARCHAR(1000)) AS hn ,
                        CAST(Root.accountid AS VARCHAR(1000)) AS hs ,
                        CAST(Root.accountname AS VARCHAR(1000)) AS hl
               FROM     tempdb.dbo.T1 Root
               WHERE    Root.ParentID IS NULL
               UNION ALL
               SELECT   Recurse.AccountId AS acid ,
                        Recurse.ParentId ParentId ,
                        Root.Hlvl + 1 AS hlvl ,
                        CAST(Root.HPa + '.' + Recurse.AccountId AS VARCHAR(1000)) AS hpa ,
                        CAST(recurse.AccountId + '.' + Root.hid AS VARCHAR(1000)) AS hid ,
                        CAST(REPLACE(recurse.AccountName, '.', '') + '.' + Root.hn AS VARCHAR(1000)) AS hn ,
                        CAST(Root.hs + '.' + Recurse.AccountName AS VARCHAR(1000)) AS hs ,
                        CAST(SPACE(root.hlvl * 4) + Recurse.AccountName AS VARCHAR(1000)) AS hl
               FROM     tempdb.dbo.T1 Recurse
                        INNER JOIN AccountHierarchy Root ON Root.AcId = Recurse.ParentId
             )
    UPDATE  tempdb.dbo.T1
    SET     HierarchyLevel = HLvl ,
            HPath = Hpa ,
            IdHierarchy = hid ,
            NameHierarchy = hn ,
            HierarchyLabel = hl ,
            HierarchySort = hs
    FROM    AccountHierarchy
    WHERE   AccountId = AcId;

SELECT  --HPath ,
        AccountId ,
        AccountName ,
        ParentId ,
        HierarchyLevel ,
        IdHierarchy ,
        NameHierarchy ,
        HierarchyLabel ,
        PARSENAME(IdHierarchy, 1) Acct1Id ,
        PARSENAME(NameHierarchy, 1) Acct1Name ,
        PARSENAME(IdHierarchy, 2) Acct2Id ,
        PARSENAME(NameHierarchy, 2) Acct2Name ,
        PARSENAME(IdHierarchy, 3) Acct3Id ,
        PARSENAME(NameHierarchy, 3) Acct3Name ,
        PARSENAME(IdHierarchy, 4) Acct4Id ,
        PARSENAME(NameHierarchy, 4) Acct4Name ,
        CustomerCount ,
        Cnt.TotalCustomerCount
FROM    tempdb.dbo.t1 Hier
        CROSS APPLY ( SELECT    SUM(CustomerCount) AS TotalCustomerCount
                      FROM      tempdb.dbo.t1
                      WHERE     HPath LIKE hier.HPath + '%'
                    ) Cnt
ORDER BY HierarchySort;

DROP TABLE tempdb.dbo.t1;
DROP TABLE tempdb.dbo.Account;