Best Practices for PL/SQL

Transcript Best Practices for PL/SQL

OPP 2007 February 28 – March 1, 2007 San Mateo Marriott San Mateo, California

An ODTUG SP* Oracle PL/SQL Programming Conference

* SP – Seriously Practical Conference ODTUG Kaleidoscope June 18 – 21, 2007 Pre-conference Hands-on Training - June 16 – 17 Hilton Daytona Beach Oceanfront Resort Daytona, Florida

WOW-Wide Open World, Wide Open Web!

Everything you need to know about collections, but were afraid to ask

Steven Feuerstein

PL/SQL Evangelist Quest Software [email protected]

How to benefit most from this seminar   Watch, listen, ask questions.

Download the training materials and supporting scripts: –

http://oracleplsqlprogramming.com/resources.html

–

"Demo zip": all the scripts I run in my class available at http://oracleplsqlprogramming.com/downloads/demo.zip

filename_from_demo_zip.sql

  Use these materials as an accelerator as you venture into new territory and need to apply new techniques.

PL/SQL Collections

  Collections are

single-dimensioned

information, similar to 3GL arrays.

lists of  They are an invaluable data structure.

–

All

PL/SQL developers should be very comfortable with collections and use them often.

Collections take some getting used to.

– They are not the most straightforward implementation of array-like structures.

– Advanced features like string indexes and multi level collections can be a challenge.

What we will cover on collections

     Review of basic functionality Indexing collections by strings Working with collections of collections MULTISET operators for nested tables Then later in the section on SQL: – Bulk processing with FORALL and BULK COLLECT – Table functions and pipelined functions Copyright 2000-2006 Steven Feuerstein - Page 6

What is a collection?

1 2 3 4 22 23

abc def sf q

...

rrr swq  A collection is an "ordered group of elements, all of the same type." (PL/SQL User Guide and Reference) – That's a very general definition; lists, sets, arrays and similar data structures are all types of collections.

– Each element of a collection may be addressed by a unique subscript, usually an integer but in some cases also a string.

– Collections are single-dimensional, but you can create collections of collections to emulate multi-dimensional structures.

Why use collections?

  Serve up complex datasets of information to non PL/SQL host environments using table functions .

 Generally, to manipulate in-program-memory lists of information. –

Much faster than working through SQL.

Dramatically improve multi-row querying, inserting, updating and deleting the contents of tables.

Combined with BULK COLLECT and FORALL....

 Emulate bi-directional cursors, which are not yet supported within PL/SQL.

Three Types of Collections

 Associative arrays (aka index-by tables) – Can be used only in PL/SQL blocks.

– Similar to hash tables in other languages, allows you to access elements via arbitrary subscript values.  Nested tables and Varrays – Can be used in PL/SQL blocks, but also can be the datatype of a column in a relational table. – Part of the object model in PL/SQL.

About Associative Arrays

 Unbounded, practically speaking. – Valid row numbers range from -2,147,483,647 to 2,147,483,647.

– This range allows you to employ the row number as an intelligent key, such as the primary key or unique index value, because AAs also are:  Sparse – Data does not have to be stored in consecutive rows, as is required in traditional 3GL arrays and VARRAYs.

 Index values can be integers or strings (Oracle9i R2 and above).

assoc_array_example.sql

About Nested Tables

 No pre-defined limit on a nested table.

– Valid row numbers range from 1 to 2,147,483,647.

 Part of object model, requiring initialization.

 Is always dense initially, but can become sparse after deletes.

 Can be defined as a schema level type and used as a relational table column type.

nested_table_example.sql

About Varrays

 Has a maximum size, associated with its type. – Can adjust the size at runtime in Oracle10g R2.

 Part of object model, requiring initialization.

 Is

always

dense; you can only remove elements from the end of a varray.

 Can be defined as a schema level type and used as a relational table column type.

varray_example.sql

How to choose your collection type

   Use associative arrays when you need to...

– Work within PL/SQL code only – Sparsely fill and manipulate the collection – Take advantage of negative index values Use nested tables when you need to...

– Access the collection inside SQL (table functions, columns in tables) – Want to perform set operations Use varrays when you need to...

– If you need to specify a maximum size to your collection – Access the collection inside SQL (table functions, columns in tables).

Wide Variety of Collection Methods

  Obtain information about the collection – COUNT returns number of rows currently defined in collection.

– EXISTS returns TRUE if the specified row is defined.

– FIRST/LAST return lowest/highest numbers of defined rows.

– NEXT/PRIOR return the closest defined row after/before the specified row.

– LIMIT tells you the max. number of elements allowed in a VARRAY.

Modify the contents of the collection – DELETE deletes one or more rows from the index-by table.

– EXTEND adds rows to a nested table or VARRAY.

– TRIM removes rows from a VARRAY.

Useful reminders for PL/SQL collections

 Memory for collections comes out of the PGA or Process Global Area – One per session, so a program using collections can consume a large amount of memory.

 Use the NOCOPY hint to reduce overhead of passing collections in and out of program units.

  Encapsulate or hide details of collection management.

Don't always fill collections sequentially. Think about how you need to manipulate the contents.

 Try to read a row that doesn't exist, and Oracle raises NO_DATA_FOUND.

mysess.pkg

sess2.sql

nocopy*.*

Data Caching with PL/SQL Tables

First access Database

Pass Data to Cache Not in cache; Request data from database

PGA

Function Data retrieved from cache Data returned to application Application Application Requests Data

Subsequent accesses

Database Data found in cache. Database is not needed.

PGA

Function Data retrieved from cache Data returned to application Application Application Requests Data

emplu.pkg

emplu.tst

Oracle9

Release 2 New indexing capabilities for associative arrays    Prior to Oracle9iR2, you could only index by BINARY_INTEGER.

You can now define the index on your associative array to be: – Any sub-type derived from BINARY_INTEGER – VARCHAR2(n), where n is between 1 and 32767 – %TYPE against a database column that is consistent with the above rules – A SUBTYPE against any of the above.

Oracle9

Release 2

Examples of New TYPE Variants

 All of the following are now valid TYPE declarations in Oracle9i Release 2 – You cannot use %TYPE against an INTEGER column, because INTEGER is

not

a subtype of BINARY_INTEGER.

DECLARE TYPE array_t1 IS TABLE OF NUMBER INDEX BY BINARY_INTEGER; TYPE array_t2 IS TABLE OF NUMBER INDEX BY PLS_INTEGER; TYPE array_t3 IS TABLE OF NUMBER INDEX BY POSITIVE; TYPE array_t4 IS TABLE OF NUMBER INDEX BY NATURAL; TYPE array_t5 IS TABLE OF NUMBER INDEX BY VARCHAR2(64); TYPE array_t6 IS TABLE OF NUMBER INDEX BY VARCHAR2(32767); TYPE array_t7 IS TABLE OF NUMBER INDEX BY employee.last_name%TYPE; TYPE array_t8 IS TABLE OF NUMBER INDEX BY types_pkg.subtype_t; Copyright 2000-2006 Steven Feuerstein - Page 18

Working with string-indexed collections

DECLARE TYPE population_type IS TABLE OF NUMBER INDEX BY VARCHAR2(64); country_population population_type; continent_population population_type; howmany NUMBER; BEGIN country_population ('Greenland') := 100000; country_population ('Iceland') := 750000;

assoc_array*.sql

assoc_array_perf.tst

howmany := country_population ('Greenland'); continent_population ('Australia') := 30000000; END;  Specifying a row via a string takes some getting used to, but if offers some very powerful advantages.

Ra

id access to data via strings

 One of the most powerful applications of this features is to construct very fast pathways to static data from within PL/SQL programs. – If you are repeatedly querying the same data from the database, why not cache it in your PGA inside collections?

 Emulate the various indexing mechanisms (primary key, unique indexes) with collections.

Demonstration package: assoc_array5.sql

Generate a caching package: genaa.sql

genaa.tst

Comparison of performance of different approaches: vocab*.*

The String Tracker package (V1)

 Another example: I need to keep track of the names of variables that I have already used in my test code generation.

IS TYPE used_aat IS TABLE OF BOOLEAN INDEX BY maxvarchar2_t; g_names_used used_aat; FUNCTION string_in_use ( value_in IN maxvarchar2_t ) RETURN BOOLEAN IS BEGIN RETURN g_names_used.EXISTS ( value_in ); END string_in_use; PROCEDURE mark_as_used (value_in IN maxvarchar2_t) IS BEGIN g_names_used ( value_in ) := TRUE; END mark_as_used; END string_tracker;

string_tracker1.*

Oracle9

Multi-level Collections

 Prior to Oracle9i, you could have collections of records or objects, but only if all fields were scalars.

– A collection containing another collection was not allowed.

 Now you can create collections that contain other collections and complex types.

– Applies to all three types of collections.

 The syntax is non-intuitive and resulting code can be quite complex.

String Tracker Version 2

 The problem with String Tracker V1 is that it only supports a single list of strings.

– What if I need to track multiple lists simultaneously or nested?

 Let's extend the first version to support multiple lists by using a string-indexed, multi level collection.

– A list of lists....

The String Tracker package (V2)

CREATE OR REPLACE PACKAGE BODY string_tracker IS TYPE used_aat IS TABLE OF BOOLEAN INDEX BY maxvarchar2_t; TYPE list_of_lists_aat IS TABLE OF used_aat INDEX BY maxvarchar2_t; g_list_of_lists list_of_lists_aat; PROCEDURE mark_as_used ( list_in IN maxvarchar2_t , value_in IN maxvarchar2_t , case_sensitive_in IN BOOLEAN DEFAULT FALSE ) IS l_name maxvarchar2_t := CASE case_sensitive_in WHEN TRUE THEN value_in ELSE UPPER ( value_in ) END; BEGIN g_list_of_lists ( list_in ) ( l_name) := TRUE; END mark_as_used; END string_tracker;

string_tracker2.*

Other multi-level collection examples

  Multi-level collections with intermediate records and objects.

multilevel_collections.sql

Emulation of multi-dimensional arrays – No native support, but can creates nested collections to get much the same effect.

– Use the UTL_NLA package (10gR2) for complex matrix manipulation.

multidim*.*  Four-level nested collection used to track arguments for a program unit.

– Automatically analyze ambiguous overloading.

ambig_overloading.sql

OTN: OverloadCheck

Encapsulate these complex structures!

 When working with multi-level collections, you can easily and rapidly arrive at completely unreadable and un-maintainable code.  What' s a developer to do?

– Hide complexity -- and all data structures -- behind small modules.

– Work with and through functions to retrieve contents and procedures to set contents.

cc_smartargs.pkb: cc_smartargs.next_overloading cc_smartargs.add_new_parameter

Oracle10g

Nested Tables unveil their MULTISET-edness

  Oracle10g introduces high-level set operations on nested tables (only).

– Nested tables are “multisets,” meaning that theoretically there is no order to their elements. This makes set operations of critical importance for manipulating nested tables. .

Oracle10g

Check for equality and inequality

 Just use the basic operators….

DECLARE TYPE clientele IS TABLE OF VARCHAR2 (64); group1 clientele := clientele ('Customer 1', 'Customer 2'); group2 clientele := clientele ('Customer 1', 'Customer 3'); group3 clientele := clientele ('Customer 3', 'Customer 1'); BEGIN IF group1 = group2 THEN DBMS_OUTPUT.put_line ('Group 1 = Group 2'); ELSE DBMS_OUTPUT.put_line ('Group 1 != Group 2'); END IF; IF group2 != group3 THEN DBMS_OUTPUT.put_line ('Group 2 != Group 3'); ELSE DBMS_OUTPUT.put_line ('Group 2 = Group 3'); END IF; END; Copyright 2000-2006 Steven Feuerstein - Page 28 10g_compare.sql

10g_compare2.sql

10g_compare_old.sql

Oracle10g

UNION, INTERSECT, MINUS

 Straightforward, with the MULTISET keyword.

BEGIN our_favorites := my_favorites MULTISET UNION dad_favorites; show_favorites ('MINE then DAD', our_favorites); our_favorites := dad_favorites MULTISET UNION my_favorites; show_favorites ('DAD then MINE', our_favorites); our_favorites := my_favorites MULTISET UNION DISTINCT dad_favorites; show_favorites ('MINE then DAD with DISTINCT', our_favorites); our_favorites := my_favorites MULTISET INTERSECT dad_favorites; show_favorites ('IN COMMON', our_favorites); END; our_favorites := dad_favorites MULTISET EXCEPT my_favorites; show_favorites ('ONLY DAD''S', our_favorites); Copyright 2000-2006 Steven Feuerstein - Page 29 10g_setops.sql

10g_string_nt.sql

10g_favorites.sql

10g*union*.sql

Turbo-charged SQL with BULK COLLECT and FORALL

 Improve the performance of multi-row SQL operations by an order of magnitude or more with bulk/array processing in PL/SQL!

CREATE OR REPLACE PROCEDURE upd_for_dept ( dept_in IN employee.department_id%TYPE IS ,newsal_in IN employee.salary%TYPE) CURSOR emp_cur IS SELECT employee_id,salary,hire_date FROM employee WHERE department_id = dept_in; BEGIN FOR rec IN emp_cur LOOP UPDATE employee SET salary = newsal_in WHERE employee_id = rec.employee_id; END LOOP; END upd_for_dept; “Conventional binds” (and lots of them!) Copyright 2000-2006 Steven Feuerstein - Page 30

Conventional Bind

Oracle server PL/SQL Runtime Engine

PL/SQL block Procedural statement executor

FOR rec IN emp_cur LOOP UPDATE employee SET salary = ...

WHERE employee_id = rec.employee_id; END LOOP; SQL Engine

Performance penalty for many “context switches”

SQL statement executor

Enter the “Bulk Bind”: FORALL

Oracle server PL/SQL Runtime Engine

PL/SQL block Procedural statement executor

FORALL indx IN list_of_emps.FIRST..

list_of_emps.LAST

UPDATE employee SET salary = ...

WHERE employee_id = list_of_emps(indx); SQL Engine

SQL statement executor

Much less overhead for context switching

Use the FORALL Bulk Bind Statement

 Instead of executing repetitive, individual DML statements, you can write your code like this: PROCEDURE upd_for_dept (...) IS BEGIN FORALL indx IN list_of_emps.FIRST .. list_of_emps.LAST

UPDATE employee SET salary = newsal_in WHERE employee_id = list_of_emps (indx); END;  Things to be aware of: – – –

You MUST know how to use collections to use this feature!

Only a single DML statement is allowed per FORALL.

New cursor attributes: SQL%BULK_ROWCOUNT returns number of rows affected by each row in array. SQL%BULK_EXCEPTIONS...

– –

Prior to Oracle10g, the binding array must be sequentially filled.

Use SAVE EXCEPTIONS to continue past errors.

bulktiming.sql

bulk_rowcount.sql

Use BULK COLLECT INTO for Queries

Declare a collection of records to hold the queried data. Use BULK COLLECT to retrieve all rows. Iterate through the collection contents with a loop.

DECLARE TYPE employees_aat IS TABLE OF employees%ROWTYPE INDEX BY BINARY_INTEGER; l_employees employees_aat; BEGIN SELECT * BULK COLLECT INTO FROM employees; l_employees FOR indx IN 1 .. l_employees.COUNT LOOP process_employee (l_employees(indx)); END LOOP; END; Copyright 2000-2006 Steven Feuerstein - Page 34

bulkcoll.sql

Limit the number of rows returned by BULK COLLECT

CREATE OR REPLACE PROCEDURE bulk_with_limit (deptno_in IN dept.deptno%TYPE) IS CURSOR emps_in_dept_cur IS SELECT * FROM emp WHERE deptno = deptno_in; TYPE emp_tt IS TABLE OF emps_in_dept_cur%ROWTYPE; emps emp_tt; BEGIN OPEN emps_in_dept_cur; LOOP FETCH emps_in_dept_cur BULK COLLECT INTO emps LIMIT 100; EXIT WHEN emps.COUNT = 0; process_emps (emps); END LOOP; END bulk_with_limit; Copyright 2000-2006 Steven Feuerstein - Page 35

bulklimit.sql

Use the LIMIT clause with the INTO to manage the amount of memory used with the BULK COLLECT operation.

WARNING!

BULK COLLECT will not raise NO_DATA_FOUND if no rows are found.

Best to check contents of collection to confirm that something was retrieved.

Tips and Fine Points

 Use bulk binds in these circumstances: – Recurring SQL statement in PL/SQL loop. Oracle recommended threshold: five rows!

 Bulk bind rules: – Can be used with any kind of collection; Collection subscripts cannot be expressions; The collections must be densely filled (pre-10gR2).

 Bulk collects: – Can be used with implicit and explicit cursors – Collection is always filled sequentially, starting at row 1.

emplu.pkg

cfl_to_bulk*.*

The Wonder Of Table Functions

   A table function is a function that you can call in the FROM clause of a query, and have it be treated as if it were a

relational table.

Table functions allow you to perform arbitrarily complex transformations of data and then make that data available through a query.

– Not everything can be done in SQL.

Combined with REF CURSORs, you can now more easily transfer data from within PL/SQL to host environments.

Building a table function

 A table function must return a nested table or varray based on a schema-defined type, or type defined in a PL/SQL package.

 The function header and the way it is called must be SQL-compatible: all parameters use SQL types; no named notation.

– In some cases (streaming and pipelined functions), the IN parameter must be a cursor variable -- a query result set.

Simple table function example

 Return a list of names as a nested table, and then call that function in the FROM clause.

CREATE OR REPLACE FUNCTION lotsa_names ( base_name_in IN VARCHAR2, count_in IN INTEGER ) RETURN names_nt IS retval names_nt := names_nt (); BEGIN retval.EXTEND (count_in); FOR indx IN 1 .. count_in LOOP retval (indx) := base_name_in || ' ' || indx; END LOOP; RETURN retval; END lotsa_names; Copyright 2000-2006 Steven Feuerstein - Page 39 SELECT column_value FROM TABLE ( lotsa_names ('Steven' , 100)) names; COLUMN_VALUE ----------- Steven 1 ... Steven 100 tabfunc_scalar.sql

Streaming data with table functions

 You can use table functions to "stream" data through several stages within a single SQL statement.

– Example: transform one row in the stocktable to two rows in the tickertable.

tabfunc_streaming.sql

Copyright 2000-2006 Steven Feuerstein - Page 40 CREATE TABLE stocktable ( ticker VARCHAR2(20), trade_date DATE, open_price NUMBER, close_price NUMBER ) / CREATE TABLE tickertable ( ticker VARCHAR2(20), pricedate DATE, pricetype VARCHAR2(1), price NUMBER) /

Streaming data with table functions - 2

 In this example, transform each row of the stocktable into two rows in the tickertable.

CREATE OR REPLACE PACKAGE refcur_pkg IS / TYPE refcur_t IS REF CURSOR RETURN stocktable%ROWTYPE; END refcur_pkg; CREATE OR REPLACE FUNCTION stockpivot (dataset refcur_pkg.refcur_t) RETURN tickertypeset ...

Use pipelined functions to enhance performance.

CREATE FUNCTION StockPivot (p refcur_pkg.refcur_t) RETURN TickerTypeSet PIPELINED  Pipelined functions allow you to return data iteratively, asynchronous to termination of the function.

– As data is produced within the function, it is passed back to the calling process/query.

 Pipelined functions can be defined to support parallel execution.

– Iterative data processing allows multiple processes to work on that data simultaneously.

Applications for pipelined functions

 Execution functions in parallel.

– In Oracle9i Database Release 2 and above, use the PARALLEL_ENABLE clause to allow your pipelined function to participate fully in a parallelized query.

– Critical in data warehouse applications.

 Improve speed of delivery of data to web pages.

– Use a pipelined function to "serve up" data to the webpage and allow users to being viewing and browsing, even before the function has finished retrieving all of the data. Copyright 2000-2006 Steven Feuerstein - Page 43

Piping rows out from a pipelined function

Add PIPELINED keyword to header Pipe a row of data back to calling block or query RETURN...nothing at all!

CREATE FUNCTION stockpivot (p refcur_pkg.refcur_t) RETURN tickertypeset PIPELINED IS out_rec tickertype := tickertype (NULL, NULL, NULL); in_rec p%ROWTYPE; BEGIN LOOP FETCH p INTO in_rec; EXIT WHEN p%NOTFOUND; out_rec.ticker := in_rec.ticker; out_rec.pricetype := 'O'; out_rec.price := in_rec.openprice; PIPE ROW (out_rec); END LOOP; CLOSE p; RETURN; END; Copyright 2000-2006 Steven Feuerstein - Page 44 tabfunc_setup.sql

tabfunc_pipelined.sql

Enabling Parallel Execution

 The table function's parameter list must consist only of a single

strongly-typed

REF CURSOR.

 Include the PARALLEL_ENABLE hint in the program header.

– Choose a partition option that specifies how the function's execution should be partitioned. – "ANY" means that the results are independent of the order in which the function receives the input rows (through the REF CURSOR).

Table functions – Summary

 Table functions offer significant new flexibility for PL/SQL developers.

 Consider using them when you...

– Need to pass back complex result sets of data through the SQL layer (a query); – Want to call a user defined function inside a query and execute it as part of a parallel query.

Collections – don't start coding without them.

 It is impossible to write modern PL/SQL code, taking full advantage of new features, unless you use collections.

– From array processing to table functions, collections are required.

 Today I offer this challenge: learn collections thoroughly and apply them throughout your backend code.

– Your code will get faster and in many cases much simpler than it might have been (though not always!).

OPP 2007 February 28 – March 1, 2007 San Mateo Marriott San Mateo, California

An ODTUG SP* Oracle PL/SQL Programming Conference

* SP – Seriously Practical Conference ODTUG Kaleidoscope June 18 – 21, 2007 Pre-conference Hands-on Training - June 16 – 17 Hilton Daytona Beach Oceanfront Resort Daytona, Florida

WOW-Wide Open World, Wide Open Web!

Best Practices for PL/SQL

Transcript Best Practices for PL/SQL

Everything you need to know about collections, but were afraid to ask

PL/SQL Collections

What we will cover on collections

What is a collection?

Why use collections?

Three Types of Collections

About Associative Arrays

About Nested Tables

About Varrays

How to choose your collection type

Wide Variety of Collection Methods

Useful reminders for PL/SQL collections

Examples of New TYPE Variants

Working with string-indexed collections

Ra

id access to data via strings

The String Tracker package (V1)

Multi-level Collections

String Tracker Version 2

The String Tracker package (V2)

Other multi-level collection examples

Encapsulate these complex structures!

Nested Tables unveil their MULTISET-edness

Check for equality and inequality

UNION, INTERSECT, MINUS

Turbo-charged SQL with BULK COLLECT and FORALL

Conventional Bind

Enter the “Bulk Bind”: FORALL

Use the FORALL Bulk Bind Statement

Use BULK COLLECT INTO for Queries

Limit the number of rows returned by BULK COLLECT

Tips and Fine Points

The Wonder Of Table Functions

Building a table function

Simple table function example

Streaming data with table functions

Streaming data with table functions - 2

Use pipelined functions to enhance performance.

Applications for pipelined functions

Piping rows out from a pipelined function

Enabling Parallel Execution

Table functions – Summary

Directory