Matthew P. Johnson, OCL2, CISDD CUNY, January OCL2 Oracle 10g: SQL & PL/SQL Session #8 Matthew P. Johnson CISDD, CUNY Fall, 2004

Matthew P. Johnson, OCL2, CISDD CUNY, January Agenda More PL/SQL: CASE statements Exception-handling Packages Execution rights DDL in PL/SQL with dynamic PL/SQL Triggers

Matthew P. Johnson, OCL2, CISDD CUNY, January Case-statements Saw if and if-else statements last time Oracle 8i added support for case stmts Two kinds:  Simple cast stmt  “searched” case stmt Also: case expressions

Matthew P. Johnson, OCL2, CISDD CUNY, January Simple case statements General form: ELSE is optional expression and results are scalars  numbers, chars, strings, etc.; not tables  Literals or vars CASE expression WHEN result1 THEN statements1 WHEN result2 THEN statements2... ELSE statements_else END CASE; CASE expression WHEN result1 THEN statements1 WHEN result2 THEN statements2... ELSE statements_else END CASE;

Matthew P. Johnson, OCL2, CISDD CUNY, January Simple case e.g. CASE employee_type WHEN 'S' THEN award_salary_bonus(employee_id); WHEN 'H' THEN award_hourly_bonus(employee_id); WHEN 'C' THEN award_commissioned_bonus(employee_id); ELSE RAISE invalid_employee_type; END CASE; CASE employee_type WHEN 'S' THEN award_salary_bonus(employee_id); WHEN 'H' THEN award_hourly_bonus(employee_id); WHEN 'C' THEN award_commissioned_bonus(employee_id); ELSE RAISE invalid_employee_type; END CASE;

Matthew P. Johnson, OCL2, CISDD CUNY, January Simple case’s ELSE clause This ELSE is optional, but if omitted, you get an implicit else clause: Run example: Can use a NULL statement in the ELSE clause ELSE RAISE CASE_NOT_FOUND; ELSE RAISE CASE_NOT_FOUND; declare x number := 1; begin case x when 2 then dbms_output.put_line('2'); … declare x number := 1; begin case x when 2 then dbms_output.put_line('2'); …

Matthew P. Johnson, OCL2, CISDD CUNY, January Searched case statement General form: Like C/Java if “switch”  “case” and “case”  “when” Only the first matching WHEN clause is executed CASE WHEN expression1 THEN statements1 WHEN expression2 THEN statements2... ELSE statements_else END CASE; CASE WHEN expression1 THEN statements1 WHEN expression2 THEN statements2... ELSE statements_else END CASE;

Matthew P. Johnson, OCL2, CISDD CUNY, January Searched case e.g. Q: Can this be implemented as a simple case? CASE WHEN salary >= AND salary <=20000 THEN give_bonus(employee_id, 1500); WHEN salary > AND salary <= THEN give_bonus(employee_id, 1000); WHEN salary > THEN give_bonus(employee_id, 500); ELSE give_bonus(employee_id, 0); END CASE; CASE WHEN salary >= AND salary <=20000 THEN give_bonus(employee_id, 1500); WHEN salary > AND salary <= THEN give_bonus(employee_id, 1000); WHEN salary > THEN give_bonus(employee_id, 500); ELSE give_bonus(employee_id, 0); END CASE;

Matthew P. Johnson, OCL2, CISDD CUNY, January Searched case e.g. CASE TRUE WHEN salary >= AND salary <=20000 THEN give_bonus(employee_id, 1500); WHEN salary > AND salary <= give_bonus(employee_id, 1000); WHEN salary > give_bonus(employee_id, 500); ELSE give_bonus(employee_id, 0); END CASE; CASE TRUE WHEN salary >= AND salary <=20000 THEN give_bonus(employee_id, 1500); WHEN salary > AND salary <= give_bonus(employee_id, 1000); WHEN salary > give_bonus(employee_id, 500); ELSE give_bonus(employee_id, 0); END CASE;

Matthew P. Johnson, OCL2, CISDD CUNY, January Case expressions Above were case statements  One statement/set of statements executed, depending on value of test expression Also have case expressions  Evaluates to some expression, depending on value of test expression Case expressions, too, come in both varieties

Matthew P. Johnson, OCL2, CISDD CUNY, January Simple case expression Simple_Case_Expression := CASE expression WHEN result1 THEN result_expression1 WHEN result2 THEN result_expression2... ELSE result_expression_else END; Simple_Case_Expression := CASE expression WHEN result1 THEN result_expression1 WHEN result2 THEN result_expression2... ELSE result_expression_else END; Searched_Case_Expression := CASE WHEN expression1 THEN result_expression1 WHEN expression2 THEN result_expression2... ELSE result_expression_else END; Searched_Case_Expression := CASE WHEN expression1 THEN result_expression1 WHEN expression2 THEN result_expression2... ELSE result_expression_else END;

Matthew P. Johnson, OCL2, CISDD CUNY, January CASE statements in SQL By the way: CASE statements are now supported in Oracle SQL itself SELECT CASE WHEN comm is null THEN 0 ELSE comm END FROM emp; SELECT CASE WHEN comm is null THEN 0 ELSE comm END FROM emp;

Matthew P. Johnson, OCL2, CISDD CUNY, January Explicit cursors v. for loop cursors DECLARE CURSOR occupancy_cur IS SELECT pet_id, room_number FROM occupancy WHERE occupied_dt = TRUNC (SYSDATE); occupancy_rec occupancy_cur%ROWTYPE; BEGIN OPEN occupancy_cur; LOOP FETCH occupancy_cur INTO occupancy_rec; EXIT WHEN occupancy_cur%NOTFOUND; update_bill (occupancy_rec.pet_id, occupancy_rec.room_number); END LOOP; CLOSE occupancy_cur; END; DECLARE CURSOR occupancy_cur IS SELECT pet_id, room_number FROM occupancy WHERE occupied_dt = TRUNC (SYSDATE); occupancy_rec occupancy_cur%ROWTYPE; BEGIN OPEN occupancy_cur; LOOP FETCH occupancy_cur INTO occupancy_rec; EXIT WHEN occupancy_cur%NOTFOUND; update_bill (occupancy_rec.pet_id, occupancy_rec.room_number); END LOOP; CLOSE occupancy_cur; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Explicit cursors v. for loop cursors DECLARE CURSOR occupancy_cur IS SELECT pet_id, room_number FROM occupancy WHERE occupied_dt = TRUNC (SYSDATE); BEGIN FOR occupancy_rec IN occupancy_cur LOOP update_bill (occupancy_rec.pet_id, occupancy_rec.room_number); END LOOP; END; DECLARE CURSOR occupancy_cur IS SELECT pet_id, room_number FROM occupancy WHERE occupied_dt = TRUNC (SYSDATE); BEGIN FOR occupancy_rec IN occupancy_cur LOOP update_bill (occupancy_rec.pet_id, occupancy_rec.room_number); END LOOP; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Another loop e.g. CREATE OR REPLACE PROCEDURE pay_out_balance ( account_id_in IN accounts.id%TYPE) -- the type of the var is the same as the field type! IS --IS or AS can be used in place of DECLARE l_balance_remaining NUMBER; BEGIN LOOP l_balance_remaining := account_balance (account_id_in); IF l_balance_remaining < 1000 THEN EXIT; -- exit from the LOOP ELSE apply_balance (account_id_in, l_balance_remaining); END IF; END LOOP; END pay_out_balance; CREATE OR REPLACE PROCEDURE pay_out_balance ( account_id_in IN accounts.id%TYPE) -- the type of the var is the same as the field type! IS --IS or AS can be used in place of DECLARE l_balance_remaining NUMBER; BEGIN LOOP l_balance_remaining := account_balance (account_id_in); IF l_balance_remaining < 1000 THEN EXIT; -- exit from the LOOP ELSE apply_balance (account_id_in, l_balance_remaining); END IF; END LOOP; END pay_out_balance;

Matthew P. Johnson, OCL2, CISDD CUNY, January Exception handlers Each WHEN-THEN names a possible exception, like a case in a switch stmt: EXCEPTION WHEN NO_DATA_FOUND THEN executable_statements1; WHEN DUP_VAL_ON_INDEX THEN executable_statements1;... WHEN OTHERS THEN otherwise_code; END; EXCEPTION WHEN NO_DATA_FOUND THEN executable_statements1; WHEN DUP_VAL_ON_INDEX THEN executable_statements1;... WHEN OTHERS THEN otherwise_code; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Function e.g. FUNCTION company_name (company_id_in IN company.company_id%TYPE) RETURN VARCHAR2 IS cname company.company_id%TYPE; BEGIN SELECT name INTO cname FROM company WHERE company_id = company_id_in; RETURN cname; EXCEPTION WHEN NO_DATA_FOUND THEN RETURN NULL; END; FUNCTION company_name (company_id_in IN company.company_id%TYPE) RETURN VARCHAR2 IS cname company.company_id%TYPE; BEGIN SELECT name INTO cname FROM company WHERE company_id = company_id_in; RETURN cname; EXCEPTION WHEN NO_DATA_FOUND THEN RETURN NULL; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Longer exception e.g. CREATE OR REPLACE PROCEDURE check_account ( account_id_in IN accounts.id%TYPE) IS l_balance_remaining NUMBER; l_balance_below_minimum EXCEPTION; l_account_name accounts.name%TYPE; BEGIN SELECT name INTO l_account_name FROM accounts WHERE id = account_id_in; l_balance_remaining := account_balance (account_id_in); DBMS_OUTPUT.put_line ('Balance for ' || l_account_name || ' = ' || l_balance_remaining); CREATE OR REPLACE PROCEDURE check_account ( account_id_in IN accounts.id%TYPE) IS l_balance_remaining NUMBER; l_balance_below_minimum EXCEPTION; l_account_name accounts.name%TYPE; BEGIN SELECT name INTO l_account_name FROM accounts WHERE id = account_id_in; l_balance_remaining := account_balance (account_id_in); DBMS_OUTPUT.put_line ('Balance for ' || l_account_name || ' = ' || l_balance_remaining);

Matthew P. Johnson, OCL2, CISDD CUNY, January Longer exception e.g. IF l_balance_remaining < 1000 THEN RAISE l_balance_below_minimum; END IF; EXCEPTION WHEN NO_DATA_FOUND THEN -- No account found for this ID log_error (...); WHEN l_balance_below_minimum THEN log_error (...); RAISE; END; IF l_balance_remaining < 1000 THEN RAISE l_balance_below_minimum; END IF; EXCEPTION WHEN NO_DATA_FOUND THEN -- No account found for this ID log_error (...); WHEN l_balance_below_minimum THEN log_error (...); RAISE; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January WHEN OTHERS and NULL Can have generic exception catcher with WHEN OTHERS To swallow all other exception types, use a null statement: EXCEPTION WHEN exception_name1 THEN --do one thing WHEN exception_name2 THEN --do another thing WHEN OTHERS THEN null; END; EXCEPTION WHEN exception_name1 THEN --do one thing WHEN exception_name2 THEN --do another thing WHEN OTHERS THEN null; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Raising exceptions You can raise an exception with RAISE: DECLARE exception_name EXCEPTION; BEGIN IF condition THEN RAISE exception_name; END IF; EXCEPTION WHEN exception_name THEN statement; END; DECLARE exception_name EXCEPTION; BEGIN IF condition THEN RAISE exception_name; END IF; EXCEPTION WHEN exception_name THEN statement; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January More on scope Can name blocks and loops with labels > BEGIN INSERT INTO catalog VALUES (...); EXCEPTION WHEN DUP_VAL_ON_INDEX THEN NULL; END insert_but_ignore_dups; > BEGIN INSERT INTO catalog VALUES (...); EXCEPTION WHEN DUP_VAL_ON_INDEX THEN NULL; END insert_but_ignore_dups;

Matthew P. Johnson, OCL2, CISDD CUNY, January Scope and nested, labeled loops > DECLARE counter INTEGER := 0; BEGIN... DECLARE counter INTEGER := 1; BEGIN IF counter = outerblock.counter THEN... END IF; END; > DECLARE counter INTEGER := 0; BEGIN... DECLARE counter INTEGER := 1; BEGIN IF counter = outerblock.counter THEN... END IF; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Scope and nested, labeled loops BEGIN > LOOP EXIT outer_loop; END LOOP; some_statement ; END LOOP; END; BEGIN > LOOP EXIT outer_loop; END LOOP; some_statement ; END LOOP; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Packages Functions and procedures (and vars) can be grouped in packages  Like Java packages, C++ namespaces, etc. A pkg has a specification and a body  Somewhat like C++ class definitions Specification: declares public functions  “public” means: can be run by a user with EXECUTE authority on this pkg Body: defines all functions  Vars defined here are visible to the pkg’s programs

Matthew P. Johnson, OCL2, CISDD CUNY, January Package e.g. Create or replace PACKAGE rg_select as list_name VARCHAR2(60); PROCEDURE init_list (item_name_in IN VARCHAR2, fill_action_in IN VARCHAR2 := 'IMMEDIATE'); PROCEDURE delete_list; PROCEDURE clear_list; END rg_select; Create or replace PACKAGE rg_select as list_name VARCHAR2(60); PROCEDURE init_list (item_name_in IN VARCHAR2, fill_action_in IN VARCHAR2 := 'IMMEDIATE'); PROCEDURE delete_list; PROCEDURE clear_list; END rg_select;

Matthew P. Johnson, OCL2, CISDD CUNY, January Package body Package body is defined separately, containing actual ftn/proc implementations  Do not preface ftns and procs with “create or replace” Create or replace PACKAGE body rg_select as PROCEDURE init_list (item_name_in IN VARCHAR2, fill_action_in IN VARCHAR2 := 'IMMEDIATE') as … End; … END rg_select; Create or replace PACKAGE body rg_select as PROCEDURE init_list (item_name_in IN VARCHAR2, fill_action_in IN VARCHAR2 := 'IMMEDIATE') as … End; … END rg_select;

Matthew P. Johnson, OCL2, CISDD CUNY, January Cursors in PL/SQL As expected, PL/SQL has syntax to do the usual things:  Declare cursors  Open and close  Fetch and eventually leave Each can be done manually Also has elegant for/cursor loop  Declare, open, close, fetch all automatic: Example:  FOR my-rec IN my-cursor LOOP … END LOOP; FOR my-rec IN my-cursor LOOP … END LOOP;

Matthew P. Johnson, OCL2, CISDD CUNY, January Record-based DML CREATE OR REPLACE PROCEDURE set_book_info ( book_in IN books%ROWTYPE) IS BEGIN INSERT INTO books VALUES book_in; EXCEPTION WHEN DUP_VAL_ON_INDEX THEN UPDATE books SET ROW = book_in WHERE isbn = book_in.isbn; END; CREATE OR REPLACE PROCEDURE set_book_info ( book_in IN books%ROWTYPE) IS BEGIN INSERT INTO books VALUES book_in; EXCEPTION WHEN DUP_VAL_ON_INDEX THEN UPDATE books SET ROW = book_in WHERE isbn = book_in.isbn; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Programs and rights By default, only the creator of a program may run it (apart from the admin) If others should run, must GRANT them permission: Permissions can be revoked: Can also grant to particular roles or everyone: Wider/narrower grant ops are independent… SQL> GRANT EXECUTE ON wordcount TO george; SQL> REVOKE EXECUTE FROM wordcount TO george; SQL> GRANT EXECUTE ON wordcount TO everyone;

Matthew P. Johnson, OCL2, CISDD CUNY, January PL/SQL v. SQL There are some things SQL can’t do (e.g., factorial), but some problems can be solved in both DECLARE CURSOR checked_out_cur IS SELECT pet_id, name, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; BEGIN FOR checked_out_rec IN checked_out_cur LOOP INSERT INTO occupancy_history (pet_id, name, checkout_date) VALUES (checked_out_rec.pet_id, checked_out_rec.name, checked_out_rec.checkout_date); DELETE FROM occupancy WHERE pet_id = checked_out_rec.pet_id; END LOOP; END; DECLARE CURSOR checked_out_cur IS SELECT pet_id, name, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; BEGIN FOR checked_out_rec IN checked_out_cur LOOP INSERT INTO occupancy_history (pet_id, name, checkout_date) VALUES (checked_out_rec.pet_id, checked_out_rec.name, checked_out_rec.checkout_date); DELETE FROM occupancy WHERE pet_id = checked_out_rec.pet_id; END LOOP; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January PL/SQL v. SQL The same thing can be done w/o a cursor: BEGIN INSERT INTO occupancy_history (pet_id, NAME, checkout_date) SELECT pet_id, NAME, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; DELETE FROM occupancy WHERE checkout_date IS NOT NULL; END; BEGIN INSERT INTO occupancy_history (pet_id, NAME, checkout_date) SELECT pet_id, NAME, checkout_date FROM occupancy WHERE checkout_date IS NOT NULL; DELETE FROM occupancy WHERE checkout_date IS NOT NULL; END;

Matthew P. Johnson, OCL2, CISDD CUNY, January Dynamic PL/SQL Saw “dynamic SQL” in the cases of Pro*C and JDBC  Ability to run ad-hoc (non-hard-coded) SQL in programs/scripts Can also do this in PL/SQL The string can be passed in, created from concatenation, etc. EXECUTE IMMEDIATE ;

Matthew P. Johnson, OCL2, CISDD CUNY, January Dynamic PL/SQL E.g.: write function to return number rows in an arbitrary table CREATE OR REPLACE FUNCTION rowCount ( tabname IN VARCHAR2) return integer as retval integer; begin execute immediate 'select count(*) from ' || tabname into retval; return retval; end; / CREATE OR REPLACE FUNCTION rowCount ( tabname IN VARCHAR2) return integer as retval integer; begin execute immediate 'select count(*) from ' || tabname into retval; return retval; end; /

Matthew P. Johnson, OCL2, CISDD CUNY, January Dynamic PL/SQL for DDL Ordinarily can’t do DDL in PL/SQL But you can in dynamic PL/SQL Here’s an e.g.: CREATE OR REPLACE procedure dropproc(procname in varchar2) as begin execute immediate 'drop procedure ' || procname; end; / CREATE OR REPLACE procedure dropproc(procname in varchar2) as begin execute immediate 'drop procedure ' || procname; end; /

Matthew P. Johnson, OCL2, CISDD CUNY, January More on PL/SQL O’Reilly’s Oracle PL/SQL Programming:   This lecture somewhat follows 3 rd edition of this book PL/SQL Reference & Tutorial:  Introduction to PL/SQL:  Oracle FAQ's Script and Code Exchange: 