为什么在PL / SQl ORACLE中使用游标？

Question

I'm a beginner at PL/SQL, and during studying the course I saw CURSOR and I want to know why we should use it, and when? thank you very much

Answer 1

When you do a SELECT and it returns more than one row you can't save the rows in a variable , so you'll have to use a CURSOR . If you are familiar with programming a CURSOR is something like an Array . So if you do a SELECT and save the results in a variable like in the code:

SELECT id INTO v_id FROM table;

and if more than one row is returned, you cant save the rows in the variable v_id , and a TOO_MANY_ROWS Exception will be thrown. Reference: http://www.oracle.com/technetwork/issue-archive/2013/13-mar/o23plsql-1906474.html

Answer 2

Also, if you've seen Oracle's FOR ... IN (SELECT ...) ... LOOP ... END LOOP statement, that's using an implicit cursor.

The reason to use the explicit cursor method is that you can do more things with the cursor, such as BULK COLLECT which can greatly improve your processing performance in many, but not all, situations. That greater control (beyond just doing BULK COLLECT) is helpful as you develop more-elaborate processes.

Good luck on your journey into Oracle. I've been using it for 14 years and am a big fan.