如果您正在查看大型商店数量，那么我强烈建议您阅读 Jeff Moden 的Hierarchies on Steroids Part #1和Part #2。他比较了将层次结构存储为邻接列表（每个孩子都有一个父外键）或嵌套集的相对优势。邻接表的优点是插入速度更快，对用户来说更直观；对于可能在层次结构上运行的许多报表，嵌套集更快。
第 1 部分提供了一种有效的面向集合的算法，用于从邻接列表中创建嵌套集层次结构表，我在此对其进行复制。它在某些领域是特定于 SQL Server 的，但应该可以帮助您在 Postgres SQL 中创建等效代码。
CREATE PROCEDURE dbo.RebuildNestedSets AS
/****************************************************************************
Purpose:
Rebuilds a "Hierarchy" table that contains the original Adjacency List,
the Nested Sets version of the same hierarchy, and several other useful
columns of data some of which need not be included in the final table.
Usage:
EXEC dbo.RebuildNestedSets
Progammer's Notes:
1. As currently written, the code reads from a table called dbo.Employee.
2. The Employee table must contain well indexed EmployeeID (child) and
ManagerID (parent) columns.
3. The Employee table must be a "well formed" Adjacency List. That is, the
EmployeeID column must be unique and there must be a foreign key on the
ManagerID column that points to the EmployeeID column. The table must not
contain any "cycles" (an EmployeeID in its own upline). The Root Node
must have a NULL for ManagerID.
4. The final table, named dbo.Hierarchy, will be created in the same
database as where this stored procedure is present. IT DOES DROP THE
TABLE CALLED DBO.HIERARCHY SO BE CAREFUL THAT IT DOESN'T DROP A TABLE
NEAR AND DEAR TO YOUR HEART.
5. This code currently has no ROLLBACK capabilities so make sure that you
have met all of the requirements (and, perhaps, more) cited in #3 above.
Dependencies:
1. This stored procedure requires that the following special purpose HTally
table be present in the same database from which it runs.
--===== Create the HTally table to be used for splitting SortPath
SELECT TOP 1000 --(4 * 1000 = VARBINARY(4000) in length)
N = ISNULL(CAST(
(ROW_NUMBER() OVER (ORDER BY (SELECT NULL))-1)*4+1
AS INT),0)
INTO dbo.HTally
FROM master.sys.all_columns ac1
CROSS JOIN master.sys.all_columns ac2
;
--===== Add the quintessential PK for performance.
ALTER TABLE dbo.HTally
ADD CONSTRAINT PK_HTally
PRIMARY KEY CLUSTERED (N) WITH FILLFACTOR = 100
;
Revision History:
Rev 00 - Circa 2009 - Jeff Moden
- Initial concept and creation.
Rev 01 - PASS 2010 - Jeff Moden
- Rewritten for presentation at PASS 2010.
Rev 02 - 06 Oct 2012 - Jeff Moden
- Code redacted to include a more efficient, higher performmance
method of splitting the SortPath using a custom HTally Table.
****************************************************************************/
--===========================================================================
-- Presets
--===========================================================================
--===== Suppress the auto-display of rowcounts to prevent from returning
-- false errors if called from a GUI or other application.
SET NOCOUNT ON;
--===== Start a duration timer
DECLARE @StartTime DATETIME,
@Duration CHAR(12);
SELECT @StartTime = GETDATE();
--===========================================================================
-- 1. Read ALL the nodes in a given level as indicated by the parent/
-- child relationship in the Adjacency List.
-- 2. As we read the nodes in a given level, mark each node with the
-- current level number.
-- 3. As we read the nodes in a given level, convert the EmployeeID to
-- a Binary(4) and concatenate it with the parents in the previous
-- level's binary string of EmployeeID's. This will build the
-- SortPath.
-- 4. Number the rows according to the Sort Path. This will number the
-- rows in the same order that the push-stack method would number
-- them.
--===========================================================================
--===== Conditionally drop the final table to make reruns easier in SSMS.
IF OBJECT_ID('FK_Hierarchy_Hierarchy') IS NOT NULL
ALTER TABLE dbo.Hierarchy
DROP CONSTRAINT FK_Hierarchy_Hierarchy;
IF OBJECT_ID('dbo.Hierarchy','U') IS NOT NULL
DROP TABLE dbo.Hierarchy;
RAISERROR('Building the initial table and SortPath...',0,1) WITH NOWAIT;
--===== Build the new table on-the-fly including some place holders
WITH cteBuildPath AS
( --=== This is the "anchor" part of the recursive CTE.
-- The only thing it does is load the Root Node.
SELECT anchor.EmployeeID,
anchor.ManagerID,
HLevel = 1,
SortPath = CAST(
CAST(anchor.EmployeeID AS BINARY(4))
AS VARBINARY(4000)) --Up to 1000 levels deep.
FROM dbo.Employee AS anchor
WHERE ManagerID IS NULL --Only the Root Node has a NULL ManagerID
UNION ALL
--==== This is the "recursive" part of the CTE that adds 1 for each level
-- and concatenates each level of EmployeeID's to the SortPath column.
SELECT recur.EmployeeID,
recur.ManagerID,
HLevel = cte.HLevel + 1,
SortPath = CAST( --This does the concatenation to build SortPath
cte.SortPath + CAST(Recur.EmployeeID AS BINARY(4))
AS VARBINARY(4000))
FROM dbo.Employee AS recur WITH (TABLOCK)
INNER JOIN cteBuildPath AS cte
ON cte.EmployeeID = recur.ManagerID
) --=== This final INSERT/SELECT creates the Node # in the same order as a
-- push-stack would. It also creates the final table with some
-- "reserved" columns on the fly. We'll leave the SortPath column in
-- place because we're still going to need it later.
-- The ISNULLs make NOT NULL columns
SELECT EmployeeID = ISNULL(sorted.EmployeeID,0),
sorted.ManagerID,
HLevel = ISNULL(sorted.HLevel,0),
LeftBower = ISNULL(CAST(0 AS INT),0), --Place holder
RightBower = ISNULL(CAST(0 AS INT),0), --Place holder
NodeNumber = ROW_NUMBER() OVER (ORDER BY sorted.SortPath),
NodeCount = ISNULL(CAST(0 AS INT),0), --Place holder
SortPath = ISNULL(sorted.SortPath,sorted.SortPath)
INTO dbo.Hierarchy
FROM cteBuildPath AS sorted
OPTION (MAXRECURSION 100) --Change this IF necessary
;
RAISERROR('There are %u rows in dbo.Hierarchy',0,1,@@ROWCOUNT) WITH NOWAIT;
--===== Display the cumulative duration
SELECT @Duration = CONVERT(CHAR(12),GETDATE()-@StartTime,114);
RAISERROR('Cumulative Duration = %s',0,1,@Duration) WITH NOWAIT;
--===========================================================================
-- Using the information created in the table above, create the
-- NodeCount column and the LeftBower and RightBower columns to create
-- the Nested Sets hierarchical structure.
--===========================================================================
RAISERROR('Building the Nested Sets...',0,1) WITH NOWAIT;
--===== Declare a working variable to hold the result of the calculation
-- of the LeftBower so that it may be easily used to create the
-- RightBower in a single scan of the final table.
DECLARE @LeftBower INT
;
--===== Create the Nested Sets from the information available in the table
-- and in the following CTE. This uses the proprietary form of UPDATE
-- available in SQL Serrver for extra performance.
WITH cteCountDownlines AS
( --=== Count each occurance of EmployeeID in the sort path
SELECT EmployeeID = CAST(SUBSTRING(h.SortPath,t.N,4) AS INT),
NodeCount = COUNT(*) --Includes current node
FROM dbo.Hierarchy h,
dbo.HTally t
WHERE t.N BETWEEN 1 AND DATALENGTH(SortPath)
GROUP BY SUBSTRING(h.SortPath,t.N,4)
) --=== Update the NodeCount and calculate both Bowers
UPDATE h
SET @LeftBower = LeftBower = 2 * NodeNumber - HLevel,
h.NodeCount = downline.NodeCount,
h.RightBower = (downline.NodeCount - 1) * 2 + @LeftBower + 1
FROM dbo.Hierarchy h
JOIN cteCountDownlines downline
ON h.EmployeeID = downline.EmployeeID
;
RAISERROR('%u rows have been updated to Nested Sets',0,1,@@ROWCOUNT)
WITH NOWAIT;
RAISERROR('If the rowcounts don''t match, there may be orphans.'
,0,1,@@ROWCOUNT)WITH NOWAIT;
--===== Display the cumulative duration
SELECT @Duration = CONVERT(CHAR(12),GETDATE()-@StartTime,114);
RAISERROR('Cumulative Duration = %s',0,1,@Duration) WITH NOWAIT;
--===========================================================================
-- Prepare the table for high performance reads by adding indexes.
--===========================================================================
RAISERROR('Building the indexes...',0,1) WITH NOWAIT;
--===== Direct support for the Nested Sets
ALTER TABLE dbo.Hierarchy
ADD CONSTRAINT PK_Hierarchy
PRIMARY KEY CLUSTERED (LeftBower, RightBower) WITH FILLFACTOR = 100
;
CREATE UNIQUE INDEX AK_Hierarchy
ON dbo.Hierarchy (EmployeeID) WITH FILLFACTOR = 100
;
ALTER TABLE dbo.Hierarchy
ADD CONSTRAINT FK_Hierarchy_Hierarchy FOREIGN KEY
(ManagerID) REFERENCES dbo.Hierarchy (EmployeeID)
ON UPDATE NO ACTION
ON DELETE NO ACTION
;
--===== Display the cumulative duration
SELECT @Duration = CONVERT(CHAR(12),GETDATE()-@StartTime,114);
RAISERROR('Cumulative Duration = %s',0,1,@Duration) WITH NOWAIT;
--===========================================================================
-- Exit
--===========================================================================
RAISERROR('===============================================',0,1) WITH NOWAIT;
RAISERROR('RUN COMPLETE',0,1) WITH NOWAIT;
RAISERROR('===============================================',0,1) WITH NOWAIT;
第 2 部分涵盖了一些预先报告需求，例如不同深度级别的子层次结构的总计：
--===== Start a "Timer" to see how long this all takes.
DECLARE @StartTime DATETIME;
SELECT @StartTime = GETDATE();
--===========================================================================
-- 1. Read ALL the nodes in a given level as indicated by the parent/
-- child relationship in the Adjacency List.
-- 2. As we read the nodes in a given level, mark each node with the
-- current level number.
-- 3. As we read the nodes in a given level, convert the EmployeeID to
-- a Binary(4) and concatenate it with the parents in the previous
-- level’s binary string of EmployeeID’s. This will build the
-- SortPath.
--===========================================================================
--===== Conditionally drop the work table to make reruns easier in SSMS.
IF OBJECT_ID('dbo.Hierarchy','U') IS NOT NULL
DROP TABLE dbo.Hierarchy;
--===== Build the new table on-the-fly including some place holders
WITH cteBuildPath AS
( --=== This is the "anchor" part of the recursive CTE.
-- The only thing it does is load the Root Node.
SELECT anchor.EmployeeID,
anchor.ManagerID,
HLevel = 1,
SortPath = CAST(
CAST(anchor.EmployeeID AS BINARY(4))
AS VARBINARY(4000)) --Up to 1000 levels deep.
FROM dbo.Employee AS anchor
WHERE ManagerID IS NULL --Only the Root Node has a NULL ManagerID
UNION ALL
--==== This is the "recursive" part of the CTE that adds 1 for each level
-- and concatenates each level of EmployeeID's to the SortPath column.
SELECT recur.EmployeeID,
recur.ManagerID,
HLevel = cte.HLevel + 1,
SortPath = CAST( --This does the concatenation to build SortPath
cte.SortPath + CAST(Recur.EmployeeID AS BINARY(4))
AS VARBINARY(4000))
FROM dbo.Employee AS recur WITH (TABLOCK)
INNER JOIN cteBuildPath AS cte
ON cte.EmployeeID = recur.ManagerID
) --=== This final INSERT/SELECT creates an iterim working table to hold the
-- original Adjacency List, the hierarchal level of each node, and the
-- SortPath which is the binary representation of each node's upline.
-- The ISNULLs make NOT NULL columns
SELECT EmployeeID = ISNULL(sorted.EmployeeID,0),
sorted.ManagerID,
Sales = ISNULL(CAST(0 AS BIGINT),0), --Place Holder
HLevel = ISNULL(sorted.HLevel,0),
SortPath = ISNULL(sorted.SortPath,sorted.SortPath)
INTO dbo.Hierarchy
FROM cteBuildPath AS sorted
OPTION (MAXRECURSION 100) --Change this IF necessary
;
--===== You'll be tempted to add the following index because it seems so
-- logical a thing to do for performance, but DON'T do it! It will
-- actually slow the rest of the code down by a factor of 2!!!!
--ALTER TABLE dbo.Hierarchy
-- ADD CONSTRAINT PK_Hierarchy PRIMARY KEY CLUSTERED (EmployeeID)
--;
--===== Populate the Hierarchy table with current Sales data.
UPDATE h
SET h.Sales = s.Sales
FROM dbo.Hierarchy h
INNER JOIN dbo.CurrentMonthlySales s
ON h.EmployeeID = s.EmployeeID
;
--===== Conditionally drop the final table to make reruns easier in SSMS.
IF OBJECT_ID('dbo.PreAggregatedHierarchy,'U') IS NOT NULL
DROP TABLE dbo.PreAggregatedHierarchy
;
--===== Now, build "Everything" into the PreAggregatedHierarchy table.
WITH
cteSplit AS
(--==== Splits the path into elements (including Sales and HLevel)
-- so that we can aggregate them by EmployeeID and HLevel.
-- Can't aggregate here without including the SortPath so we don't.
SELECT EmployeeID = CAST(SUBSTRING(h.SortPath,t.N,4) AS INT),
h.HLevel, h.Sales
FROM dbo.HTally AS t
CROSS JOIN dbo.Hierarchy AS h
WHERE t.N BETWEEN 1 AND DATALENGTH(SortPath)
),
cteAggregate AS
(--==== Creates the aggregates and introduces the "Relative Level" column.
-- NodeCount = Count of nodes in downline for each EmployeeID by Level
-- Sales = Total Sales in downline for each EmployeeID by Level.
SELECT EmployeeID,
HLevel,
RLevel = ROW_NUMBER() OVER (PARTITION BY EmployeeID
ORDER BY EmployeeID, HLevel),
NodeCount = COUNT(*),
Sales = SUM(CAST(Sales AS MONEY))
FROM cteSplit
GROUP BY EmployeeID, HLevel
)
--===== Adds a "Rollup" to create all the subtotals that we need.
-- We couldn't do this in the previous step because we didn't know what
-- the "Relative Level" was for each row, yet.
-- The HAVING eliminates unnecessary subtotals that are created.
SELECT EmployeeID = ISNULL(a.EmployeeID,0), --Convert NULL total lines to 0
HLevel = MIN(a.HLevel), --Just so we don't have to GROUP BY
RLevel = ISNULL(CAST(a.RLevel AS TINYINT),0),
NodeCount = SUM(a.NodeCount), --Just so we don't have to GROUP BY
Sales = SUM(a.Sales) --Just so we don't have to GROUP BY
INTO dbo.PreAggregatedHierarchy
FROM cteAggregate a
GROUP BY EmployeeID, RLevel WITH ROLLUP
HAVING EmployeeID > 0 --Eliminates the NULL total lines for cleaner output
;
--===== Add the Clustered Index as a Primary Key
ALTER TABLE dbo.PreAggregatedHierarchy
ADD CONSTRAINT PK_PreAggregatedHierarchy
PRIMARY KEY CLUSTERED (EmployeeID, RLevel) WITH FILLFACTOR = 100
;
--===== Display how long it all took
PRINT 'Duration: ' + CONVERT(CHAR(12),GETDATE()-@StartTime,114) + ' (hh:mi:ss:mmm)';
您计算简单下线计数的特定问题简化为关于 Jeff 术语嵌套集表中每个节点的左凉亭和右凉亭的简单算术计算，如下所示：
Children = (RightBower - 1 - LeftBower) / 2