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PL/SQL recursive calls:  recursion in Oracle

Oracle Tips by Burleson Consulting

Question:  Does Oracle PL/SQL support recursive calls.  I mean, can I use recursion to have a function call itself?


Answer:
Yes, PL/SQL does support recursion via function calls.  Recursion is the act of a function calling itself, and a recursive call requires PL/SQL to create local copies of its memory structures for each call.  The Oracle docs notes:

?PL/SQL does allow for recursive execution of function calls, however, so you can put it to use inside a SQL statement where recursion is needed.?

The PL/SQL User's Guide and Reference notes:

"A recursive subprogram is one that calls itself. Each recursive call creates a new instance of any items declared in the subprogram, including parameters, variables, cursors, and exceptions.

Likewise, new instances of SQL statements are created at each level in the recursive descent."

See here for an example of recursive PL/SQL calls.

PL/SQL Recursive cursors

A "cursor" is not a PL/SQL programmer who cusses, but rather, PL/SQL uses a cursor to keep a handle to each recursive call.  In PL/SQL, a recursive cursor (a pointer to a shared SQL area) is used to keep a pointer to each call of a recursive function in PL/SQL.

Recursive SQL

A ?Recursive SQL statement? refers to additional "hidden" SQL that is issued for internal Oracle functions such as re-caching paged-out data from the dictionary cache, but we also see recursive SQL for these items, especially DDL:

  • Parsing a new SQL statement (validate table & column names, check security)
     

  • Space management functions required to service DDL (create table)
     

  • Trigger code
     

  • SQL within PL/SQL (functions and stored procedures)
     

  • Referential integrity checks

 

For more examples of using recursion with PL/SQL, see the outstanding book "Oracle PL/SQL Tuning: Expert Secrets for High Performance Programming" by Dr. Tim Hall, Oracle ACE of the year, 2006:

 
If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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