Nested Sets

Kevin Feasel

2017-01-04

T-SQL

Nate Johnson explains the nested sets model:

Put another way, the #3 rule is that you should always operate on the tree (CrUD ops) using stored-procedures and/or triggers that encapsulate all the nitty-gritty details of maintaining the correct position values during said insert/update/delete operations.  Of course, somebody is responsible for writing those stored-procs.  Any volunteers?  Easy now, don’t raise your hands all at once!  Generally, this responsibility falls to the DBA(s) or DBDev(s).

The problem at-hand, in my current situation, was that of “moving a sub-tree”, i.e. taking a node and all its descendants, and moving it to place it under another “parent” node.  In some models, and/or in some languages, this is a simple recursive operation.  However, SQL is not spectacular at recursion — after all, we’re working in a relational engine — so let’s try to play to its strengths:

This is a straightforward look at one of the major hierarchical models in relational design.  Well worth a look.

Related Posts

HASHBYTES On FOR JSON PATH Data

Greg Low walks us through a mechanism to check whether data has changed: In a previous post, I wrote about how to determine if a set of incoming values for a row are different to all the existing values in the row, using T-SQL in SQL Server. I later remembered that I’d seen a message by Adam […]

Read More

Parallelism Strategies For Grouping Operations

Itzik Ben-Gan continues his series on grouping data in SQL Server by looking at how these operations can go parallel: Besides needing to choose between various grouping and aggregation strategies (preordered Stream Aggregate, Sort + Stream Aggregate, Hash Aggregate), SQL Server also needs to choose whether to go with a serial or a parallel plan. […]

Read More

1 Comment

  • Nate_the_DBA on 2017-01-04

    Thank you so much for the pingback! It’s truly an honor to be mentioned in your blog, my good sir.

Comments are closed

Categories

January 2017
MTWTFSS
« Dec Feb »
 1
2345678
9101112131415
16171819202122
23242526272829
3031