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Example: find Bart’s ancestors. “Ancestor” has a recursive definition. ! is "’s ancestor if. ! is "’s parent, or. ! is #’s ancestor and # is "’s ancestor. Recursion in SQL. SQL2 had no recursion. You can find Bart’s parents, grandparents, great grandparents, etc.
Recursion in SQL. SQL2 had no recursion. You can find Bart’s parents, grandparents, great grandparents, etc. SELECT p1.parent AS grandparent FROM Parent p1, Parent p2 WHERE p1.child = p2.parent AND p2.child = 'Bart'; But you cannot find all his ancestors with a single query. SQL3 introduces recursion. WITH clause.
recursion: each RECURSIVE definition has at most one reference to a recursively-defined table • Can we make the ancestor query linear? WITH RECURSIVE Ancestor(ancestor, descendent) AS (SELECT * FROM ParentChild) UNION (SELECT parent, descendent FROM ParentChild, Ancestor WHERE child = ancestor) SELECT ancestor FROM Ancestor WHERE descendent ...
One way to accomplish this is with a SQL feature called recursive queries. Let's take a real-life example. Let's assume we've got a database with a list of nodes and a list of links between them (you can think of them as cities and roads). Our task is to find the shortest path from node 1 to node 6.
14 Σεπ 2022 · The post will not go into the details of those many use cases, rather it will examine two hypothetical examples designed to help you understand the concept — the simplest possible case of recursion in numbers and querying data from the family tree. Recursive SQL: What Does It Mean and How Does It Work?
26 Σεπ 2024 · The optional RECURSIVE modifier changes WITH from a mere syntactic convenience into a feature that accomplishes things not otherwise possible in standard SQL. Using RECURSIVE, a WITH query can refer to its own output. A very simple example is this query to sum the integers from 1 through 100:
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