By Joe Celko
In the early days of SQL, one of the objections to the relational approach to data was that it could not handle hierarchies and tree structures. In those days, IMS from IBM was the major storage tool in large corporations. It still is.
IMS is a pure tree structure that the user navigates. This was the basis for all serious, large-scale DP work, so people assumed that if SQL could not handle such structures, it would never be a serious production tool. You might use it for a reporting tool or something off to the side, but not as the main database for the enterprise.
Well, IMS is still out there and it holds a lot of data, but SQL has moved into serious production databases. As it turned out, the problem was not that SQL could not model hierarchies. The problem was programmers had to learn how to model hierarchies. New tools are like that; you surprise yourself when you finally get the feel for them.
There are many different ways to represent trees in SQL and this short article discusses one of them. This material is taken, slightly modified, from Chapter 3 of my new book, Trees & Hierarchies in SQL for Smarties from Morgan-Kaufmann Publishers.
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In the early days of SQL, one of the objections to the relational approach to data was that it could not handle hierarchies and tree structures. In those days, IMS from IBM was the major storage tool in large corporations. It still is.
IMS is a pure tree structure that the user navigates. This was the basis for all serious, large-scale DP work, so people assumed that if SQL could not handle such structures, it would never be a serious production tool. You might use it for a reporting tool or something off to the side, but not as the main database for the enterprise.
Well, IMS is still out there and it holds a lot of data, but SQL has moved into serious production databases. As it turned out, the problem was not that SQL could not model hierarchies. The problem was programmers had to learn how to model hierarchies. New tools are like that; you surprise yourself when you finally get the feel for them.
There are many different ways to represent trees in SQL and this short article discusses one of them. This material is taken, slightly modified, from Chapter 3 of my new book, Trees & Hierarchies in SQL for Smarties from Morgan-Kaufmann Publishers.
Read More/Download
