Oracle cursor for updating in oracle International hot chat without login
This upper limit is specified when the varray type is declared; it can also be modified afterward, if you are using Oracle Database 10 Release 2 or higher.
Listing 2 shows how to define a varray type and declare a variable based on this type.
The result is too many context switches and generally awful performance.
Instead, use BULK COLLECT to fetch the data into one or more collections, then use FORALL to do the DML operations in bulk.
Code Listing 3: sing a varray to ensure a limited number of rows DROP TABLE training_months / CREATE TABLE training_months (month_name VARCHAR2(100)) / BEGIN /* No trainings in the depths of summer and winter...
*/ INSERT INTO training_months VALUES (' March'); INSERT INTO training_months VALUES (' April'); INSERT INTO training_months VALUES (' May'); INSERT INTO training_months VALUES (' June'); INSERT INTO training_months VALUES (' September'); INSERT INTO training_months VALUES (' October'); INSERT INTO training_months VALUES (' November'); COMMIT; END; / DECLARE TYPE at_most_twelve_t IS VARRAY (12) OF VARCHAR2 (100); l_months at_most_twelve_t; BEGIN SELECT month_name BULK COLLECT INTO l_months FROM training_months; FOR indx IN 1 .. COUNT LOOP DBMS_OUTPUT.put_line (l_months (indx)); END LOOP; END; / However, there’s one concern with this varray approach: what if you know the maximum number of elements that can appear in the varray and that maximum is 1,000,000?
Let’s take a closer look at these five cursor FOR loop recommendations.
Never use a cursor FOR loop if the loop body executes non-query DML (INSERT, UPDATE, DELETE, MERGE).
Code Listing 1: Encapsulating SELECT INTO in a function PACKAGE employees_qp IS FUNCTION last_name (id_in IN employees.employee_id%TYPE) RETURN employees.last_name%TYPE; END employees_qp; PROCEDURE process_employee (id_in IN employees.employee_id%TYPE) IS l_last_name employees.last_name%TYPE; BEGIN l_last_name := employees_qp.last_name (id_in); END process_employee; With this approach, you are much more likely to reuse that SELECT INTO rather than write it repeatedly in your code.
Even when the query itself is automatically optimized to return 100 rows with each fetch, the INSERT or UPDATE will happen on a row-by-row basis.
This is one of the worst performance “anti-patterns” in database programming.
If you try to add a 13th month to this list, Oracle Database will raise an exception: Code Listing 2: Defining a varray type and declaring a variable DECLARE TYPE at_most_twelve_t IS VARRAY (12) OF VARCHAR2 (100); l_months at_most_twelve_t := at_most_twelve_t (' January' , ' February' , ' March' , ' April' , ' May' , ' June' , ' July' , ' August' , ' September' , ' October' , ' November' , ' December' ); Varrays offer a very nice mechanism when you need to retrieve multiple rows of data efficiently and the number of rows should never exceed a certain limit.
Suppose, for example, that I have a table (training_months) of the months in a year in which I am available to provide training on the PL/SQL language.