Download Joe Celko's Trees and Hierarchies in SQL for Smarties, (The by Joe Celko PDF
By Joe Celko
Joe Celko's bushes and Hierarchies in SQL is an intermediate to advanced-level practitioner’s advisor to studying the 2 so much hard features of constructing database functions in SQL. during this ebook, Celko illustrates numerous significant methods to representing bushes and hierarchies and comparable issues that are meant to be of curiosity to the operating database programmer. those issues comprise hierarchical encoding schemes, graphs, IMS, binary bushes, and extra. This booklet covers SQL-92 and SQL:1999.
Read or Download Joe Celko's Trees and Hierarchies in SQL for Smarties, (The Morgan Kaufmann Series in Data Management Systems) PDF
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Extra info for Joe Celko's Trees and Hierarchies in SQL for Smarties, (The Morgan Kaufmann Series in Data Management Systems)
There is a reason for setting this up as a VIEW and including the (lft, rgt) numbers of the children. member); In the nested sets model, queries based on subtrees are usually easier to write than those for individual nodes or other subsets of the tree. 4).
That gives us the effect of having a constraint to check for one NULL: CHECK((SELECT COUNT(*) FROM OrgChart WHERE boss_emp_nbr IS NULL) = 1) This is a necessary condition, but it is not a sufficient one. Consider this data, in which ‘Donna’ and ‘Eddie’ are in a cycle, and that cycle is not in the tree structure. 24 CHAPTER 2: ADJACENCY LIST MODEL emp_name boss_name 'Albert' NULL 'Bert' 'Albert' 'Chuck' 'Albert' 'Donna' 'Eddie' 'Eddie' 'Donna' One approach would be to remove all the leaf nodes and repeat this procedure until the tree is reduced to an empty set.
1 Albert 1 2 12 Chuck Bert 3 4 6 7 Donna 5 11 Fred Eddie 8 9 10 47 Nested Set Model of Hierarchies Fig. 2 Albert Chuck Eddie Donna Bert Fred As nested circles Fig. 3 Albert 9 10 Bert Chuck Donna 1 2 3 4 5 Eddie 6 7 Fred 8 9 10 11 12 As intervals on a number line If that mental model does not work for you, visualize the nested sets model as a little worm with a Bates automatic numbering stamp crawling along the “boxes-and-arrows” version of the tree. The worm starts at the top, the root, and makes a complete trip around the tree.