Tuesday, March 1, 2011

WHERE CURRENT OF in oracle plsql

WHERE CURRENT OF Clause inside the cursor

PL/SQL provides the WHERE CURRENT OF clause for both UPDATE and DELETE statements inside a cursor in order to allow you to easily make changes to the most recently fetched row of data.

The most important advantage to using WHERE CURRENT OF where you need to change the row fetched last is that you do not have to code in two (or more) places the criteria used to uniquely identify a row in a table. Without WHERE CURRENT OF, you would need to repeat the WHERE clause of your cursor in the WHERE clause of the associated UPDATEs and DELETEs. As a result, if the table structure changes in a way that affects the construction of the primary key, you have to make sure that each SQL statement is upgraded to support this change. If you use WHERE CURRENT OF, on the other hand, you only have to modify the WHERE clause of the SELECT statement.

This might seem like a relatively minor issue, but it is one of many areas in your code where you can leverage subtle features in PL/SQL to minimize code redundancies. Utilization of WHERE CURRENT OF, %TYPE, and %ROWTYPE declaration attributes, cursor FOR loops, local modularization, and other PL/SQL language constructs can have a big impact on reducing the pain you may experience when you maintain your Oracle-based applications.

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