1. SAGE Computing Services Customised Oracle Training Workshops and Consulting Are you making the most of PL/SQL? Hints and tricks and things you may have forgotten Kate Marshall Systems Consultant

2. Making the most of PL/SQL Bulk binds Implicit cursors Table functions Reminders NOCOPY Scalar subqueries Functions in the WITH clause PGA Using PL/SQL when we should just use SQL

3. Making the most of PL/SQL Bulk binds Implicit cursors Table functions Reminders NOCOPY Scalar subqueries Functions in the WITH clause PGA Using PL/SQL when we should just use SQL

4. Oracle Server PL/SQL Runtime Engine SQL Runtime Engine PL/SQL Block Procedural statement executor SQL statement executor FOR r_rec IN c_rec LOOP UPDATE emp SET salary = salary * 1.1 WHERE empno = r_rec.empno; END LOOP;

5. Bulk Binding We can use bulk binding to pass collections of rows between the SQL engine and PLSQL engine –Reduce overheads from context switching –If a single DML statement is not possible and you need to process many rows individually use bulk binds. –If the collection has 20 elements, bulk binding lets you perform the equivalent of 20 SELECT, INSERT, UPDATE, or DELETE statements using a single operation. BULK COLLECT –SELECT statements that fetch multiple rows with a single fetch into a collection before returning to the PLSQL engine FORALL –DML statements that use collections to change multiple rows –The keyword FORALL lets you run multiple DML statements very efficiently. It can only repeat a single DML statement, unlike a general- purpose FOR loop.

6. BULK COLLECT –SELECT statements that fetch multiple rows with a single fetch into a collection before returning to the PLSQL engine FORALL –DML statements that use collections to change multiple rows

7. Cursor FOR Loop There are occasions when a cursor FOR loop is better than a BULK COLLECT –When you are performing complex processing on each row within the loop, and perhaps need to exit the loop processing –BULK COLLECT will use up PGA memory to store the collections. FETCH employees_cur BULK COLLECT INTO l_employee_ids LIMIT 100;

8. Implicit v Explicit Cursors EXPLICIT -Declare cursor -Open loop -Open cursor -Fetch cursor -Close cursor -End Loop IMPLICIT -Open loop -Execute cursor -End Loop

9. Implicit v Explicit Cursors - PL/SQL is an interpreted language so every extra line of code adds to the total processing time. - Choose EXPLICIT only if you are planning to reuse the cursor

10. Table Functions Data Loading INSERT INTO employees_new (emp_no, first_name, last_name, salary) SELECT emp_no, first_name, last_name, salary FROM TABLE(emppivot_pkg.pipe_emp(CURSOR(SELECT * FROM employees))); FUNCTION pipe_emp(p_source_data IN emppivot_pkg.emptable_rct ) RETURN emppivot_ntt PIPELINED;

11. Table Functions Data Loading INSERT INTO employees_new (emp_no, first_name, last_name, salary) SELECT emp_no, first_name, last_name, salary FROM TABLE(emppivot_pkg.pipe_emp(CURSOR(SELECT * FROM employees))); FUNCTION pipe_emp(p_source_data IN emppivot_pkg.emptable_rct ) RETURN emppivot_ntt PIPELINED; Avoid Report Redundancy –Remove the need for similar Apex IR reports –Move the complexity of the query into a database function that determines the query required and returns a collection back to the TABLE function

12. Reminders Short circuit evaluation –COALESCE v NVL SELECT NVL(expr1, expr2) FROM some_table; SELECT COALESCE(expr1, expr2,..., exprN) FROM some_table;

13. Reminders Short circuit evaluation –COALESCE v NVL SELECT NVL(expr1, expr2) FROM some_table; SELECT COALESCE(expr1, expr2,..., exprN) FROM some_table; –CASE CASE when n_numb = 1 then v_status := ‘very small’; when n_numb 4 then v_status := ‘large’; else v_status := ‘very large’; END CASE;

14. Reminders Short circuit evaluation –COALESCE v NVL SELECT NVL(expr1, expr2) FROM some_table; SELECT COALESCE(expr1, expr2,..., exprN) FROM some_table; –CASE CASE when n_numb = 1 then v_status := ‘very small’; when n_numb 4 then v_status := ‘large’; else v_status := ‘very large’; END CASE; Group related subprograms into packages

15. Reminders Avoid implicit datatype conversions –Speed

16. Reminders Avoid implicit datatype conversions –Speed –Error WHERE job_no = 1311100; CREATE TABLE job ( job_no VARCHAR2(12)...

17. Reminders Avoid implicit datatype conversions –Speed –Error –Incorrect

18. Reminders Function Based Indexes Use subselects to reduce unnecessary function calls.

19. NOCOPY OUT and IN OUT parameters passed by value

20. Scalar Subqueries SELECT clause WHERE clause

21. Functions in the WITH CLAUSE

22. PGA Memory Issues The Program Global Area is used to hold: –Bind variables –PL/SQL arrays –SQL work areas (hash operations, sorting) –Cursors and cursor state information Our extra use of collections will use extra PGA memory Ensure that the PGA memory size is appropriate to actions being performed Remember the LIMIT clause when using bulk binds

23. Using PLSQL when you should just use SQL Regular Expressions –Remove unnecessary loops, functions and conditional processing with regular expressions https://regex101.com/

26. v_string 'www.sagecomputing.com.au' SELECT :v_string, LEVEL AS element_no, REGEXP_SUBSTR(:v_string, '[^\.]+', 1, LEVEL) AS single_element FROM dual CONNECT BY LEVEL <= REGEXP_COUNT(:v_string, '\.') + 1;

27. Using PLSQL when you should just use SQL Methods previously mentioned can reduce context switching load. Many advanced data operations can be done without using PL/SQL and are readily available as a SQL built-in function.

28. ROLLUP and CUBE These two operators allow a select statement to calculate totals and a grand total at any level Totals for Job and Stage Job Grand Total

29. CUBE Totals for Job and Stage Job Grand Total Job and Trade Stage and Trade Stage Total Trade Total

30. CUBE Totals for Job and Stage Job Grand Total Job and Trade Stage and Trade Stage Total Trade Total

31. Other Analytic Functions RANK and DENSE RANK RATIO_TO_REPORT LAG and LEAD LISTAGG

32. Other Analytic Functions RANK and DENSE RANK RATIO_TO_REPORT LAG and LEAD LISTAGG

33. Other Analytic Functions RANK and DENSE RANK RATIO_TO_REPORT LAG and LEAD LISTAGG

34. Other Analytic Functions RANK and DENSE RANK RATIO_TO_REPORT LAG and LEAD LISTAGG

35. Making the most of PL/SQL Bulk binds Implicit cursors Table functions Reminders NOCOPY Scalar subqueries Functions in the WITH clause PGA Using PL/SQL when we should just use SQL

36. Making the most of PL/SQL Bulk binds Implicit cursors Table functions Reminders NOCOPY Scalar subqueries Functions in the WITH clause PGA Using PL/SQL when we should just use SQL

37. SAGE Computing Services Customised Oracle Training Workshops and Consulting Presentations are available from our website: http://www.sagecomputing.com.au enquiries@sagecomputing.com.au kate.marshall@sagecomputing.com.au