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  Oracle Tips by Burleson

NOCOPY Clause

The final point to cover in passing variables  is the NOCOPY clause .  When a parameter is passed as an IN variable, it is passed by reference.  Since it will not change, PL/SQL uses the passed variable in the procedure/function.  When variables are passed in OUT or INOUT mode, a new variable is define, and the value is copied to the passed variable when the procedure ends.  If the variable is a large structure such as a PL/SQL table or an array, the application could see a performance degradation cause by copying this structure. 

The NOCOPY clause tells to PL/SQL engine to pass the variable by reference, thus avoiding the cost of copying the variable at the end of the procedure.  The PL/SQL engine has requirements that must be met before passing the variable by reference and if those requirements are not met, the NOCOPY clause will simply be ignored by the PL/SQL engine.

Important note:  If an OUT or INOUT variable is passed by reference (NOCOPY) and the procedure terminates due to an unhandled exception (ends abnormally), the value of the referenced variable may no longer be valid.

Both stored procedures and functions are passed variables, the only difference is that a function can only be passed IN variables because a function returns a value.


The above book excerpt is from:

Easy Oracle PL/SQL Programming

Get Started Fast with Working PL/SQL Code Examples

ISBN 0-9759135-7-3   

John Garmany 

http://www.rampant-books.com/book_2005_1_easy_plsql.htm

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