Oracle Class VI. Exception Block Cursors For Loops

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Alban McDaniel
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1 Oracle Class VI Exception Block Cursors For Loops

2 Pl/sql some more basics Loop through records, manipulating them one at a time. Keep code secure by offering encryption, and storing code permanently on the server rather than the client. Handle exceptions. Work with variables, parameters, collections, records, arrays, objects, cursors, exceptions, BFILEs, etc. Pl/SQL is first compiled and stored and then interpreted Reminder : use of ed

3 Exception blocks CREATE OR REPLACE FUNCTION getname (vsal number) RETURN varchar2 IS query_str VARCHAR2(1000); vename varchar2(100); BEGIN query_str := 'SELECT ename FROM emp' ' where sal= ' vsal; EXECUTE IMMEDIATE query_str INTO vename; query_str := vename ' gets ' vsal; RETURN query_str; EXCEPTION WHEN NO_DATA_FOUND THEN END; / RETURN 'NOT FOUND';

4 Some exceptions ORA-1403 NO_DATA_FOUND No data found. ORA-1422 TOO_MANY_ROWS A SELECT.INTO statement matches more than one row. ORA-1476 ZERO_DIVIDE Division by zero. ORA-1722 INVALID_NUMBER Conversion to a number failed; for example, 1A is not valid. ORA-6502 VALUE_ERROR Truncation, arithmetic, or conversion error.

5 User defined exceptions DECLARE -- Exception to indicate an error condition e_duplicateauthors EXCEPTION; RAISE e_duplicateauthors; EXCEPTION WHEN e_duplicateauthors THEN WHEN OTHERS THEN

6 Packages Stored functions and procedures may be compiled individually, or they may be grouped together into packages. Packages are loaded into memory as a whole, increasing the likelihood that a procedure or function will be resident in memory when called. Packages can include private elements, allowing logic to be hidden from view. Placing functions and procedures inside packages eliminates the need to recompile all functions and procedures that reference a newly recompiled function/procedure. Function and procedure names may be overloaded within packages, whereas standalone functions and procedures cannot be overloaded.

7 Loops DECLARE v_count PLS_INTEGER := 0; BEGIN LOOP DBMS_OUTPUT.PUT_LINE('Ah -- Much better'); v_count := v_count + 1; EXIT WHEN v_count = 20; END; / FOR counter IN low_number.. high_number LOOP action; WHILE condition LOOP action;

8 For Loop and DECLARE i NUMBER := 5; BEGIN FOR i IN 1..3 LOOP DBMS_OUTPUT.PUT_LINE ('Inside loop, i is ' TO_CHAR(i)); DBMS_OUTPUT.PUT_LINE ('Outside loop, i is ' TO_CHAR(i)); END; / DECLARE v_count PLS_INTEGER := 1; BEGIN WHILE v_count <= 20 LOOP DBMS_OUTPUT.PUT_LINE('While loop iteration: ' v_count); v_count := v_count + 1; END;

9 Cursor A cursor provides a subset of data, defined by a query, retrieved into memory when opened, and stored in memory until the cursor is closed. If data is added, deleted, or modified after the cursor is opened, the new or changed data is not reflected in the cursor result set. Declaration of a cursor: CURSOR author_cur1 IS SELECT rowid FROM authors WHERE id > 50; Opening a cursor OPEN author_cur1;

10 Cursor %FOUND The %FOUND attribute tests whether a FETCH returned a record. The return value is of Boolean type. If TRUE, a row was returned by the FETCH. If FALSE, a row was not returned. %ISOPEN This attribute tests to see if a cursor is already open.if TRUE, the cursor is open. If FALSE, it is not open. %NOTFOUND %NOTFOUND is the opposite of %FOUND. It returns TRUE if a row was not returned by the FETCH and FALSE if one was returned. %ROWCOUNT This tests for the number of rows fetched from the cursor at any given time and returns a number.

11 Cursor Contd. Use a cursor in a loop Opening a loop: LOOP Fetch: FETCH auth_cur INTO v_first_name, v_last_name, v_book_count; Exit: EXIT WHEN auth_cur%notfound; End Loop Close Cursor CLOSE auth_cur;

12 Example of a simple cursor CREATE OR REPLACE PROCEDURE compile_warning AS v_title VARCHAR2(100); CURSOR dbms_warning_cur IS SELECT title FROM books; BEGIN OPEN dbms_warning_cur; LOOP FETCH dbms_warning_cur INTO v_title; EXIT WHEN dbms_warning_cur%notfound; DBMS_OUTPUT.PUT_LINE('Titles Available: ' v_title); CLOSE dbms_warning_cur; END;

13 Assignments Write a simple procedure, which executed now will return the time that of two hours earlier. For emp table in scott, write a stored procedure that creates a table for each unique department_id and stores the employee records that belong to that particular department. Create a stored procedure which given a table name will display the name of the constraints available for the table. Handle all possible type of exception Write a simple procedure, similar to previous assignments, given an id, this displays username and domain respectively, have correct messages displayed.

D a t a b a s e M a n a g e m e n t S y s t e m L a b Institute of Engineering and Management

D a t a b a s e M a n a g e m e n t S y s t e m L a b Institute of Engineering and Management Institute of Engineering and Management Department of Computer Science and Engineering Database Management Laboratory (CS 691) Lab Manual Syllabus: Database Management System Lab Code: CS691 Contact: 3P