Walking the Table Hierarchy in Microsoft SQL Server Database

When you need to manage a set of tables in Microsoft SQL Server, it’s good to know the required order of operations. The order could be hard-coded into the process but such approaches tend to fail when the database schema evolves. Instead, I prefer to use the catalog view named [sys].[foreign_keys] to discover the relationships between tables dynamically. Long ago, I wrote a function called [LoadLevels] that I’ve used in hundreds of processes to make them reusable and more resilient. The code for that function is shown in Listing 1:

-- ==========================================================================
-- Description: Get the load levels by tracing foreign keys in the database.
-- License:     Creative Commons (Free / Public Domain)
-- Rights:      This work (Linchpin People LLC Database Load Levels Function,
--              by W. Kevin Hazzard), identified by Linchpin People LLC, is
--              free of known copyright restrictions.
-- Warranties:  This code comes with no implicit or explicit warranties.
--              Linchpin People LLC and W. Kevin Hazzard are not responsible
--              for the use of this work or its derivatives.
-- ==========================================================================
CREATE FUNCTION [dbo].[LoadLevels]()
RETURNS @results TABLE
(
[SchemaName] SYSNAME,
[TableName] SYSNAME,
[LoadLevel] INT
)
AS
BEGIN
WITH [key_info] AS
(
SELECT
[parent_object_id] AS [from_table_id],
[referenced_object_id] AS [to_table_id]
FROM [sys].[foreign_keys]
WHERE
[parent_object_id] <> [referenced_object_id]
AND [is_disabled] = 0
),
[level_info] AS
(
SELECT -- anchor part
[st].[object_id] AS [to_table_id],
0 AS [LoadLevel]
FROM [sys].[tables] AS [st]
LEFT OUTER JOIN [key_info] AS [ki] ON
[st].[object_id] = [ki].[from_table_id]
WHERE [ki].[from_table_id] IS NULL
UNION ALL
SELECT -- recursive part
[ki].[from_table_id],
[li].[LoadLevel] + 1
FROM [key_info] AS [ki]
INNER JOIN [level_info] AS [li] ON
[ki].[to_table_id] = [li].[to_table_id]
)
INSERT @results
SELECT
OBJECT_SCHEMA_NAME([to_table_id]) AS [SchemaName],
OBJECT_NAME([to_table_id]) AS [TableName],
MAX([LoadLevel]) AS [LoadLevel]
FROM [level_info]
GROUP BY [to_table_id];
RETURN
END
GO

Via.