The PL/SQL Collections Resource Center

Collections (Oracle PL/SQL's data structure to implement arrays, lists, stacks, queues, etc.) are not only handy in and of themselves, but are used for many key features of this powerful database programming language, including:

High performance querying with BULK COLLECT
Super-fast, bulk non-query DML operations with FORALL
Table functions (functions that can be treated like a table in a SELECT's FROM clause)

PL/SQL offers three types of collections - associative arrays, nested tables, and varrays - each with their own characteristics and ideal use cases.

If you are not already using collections on a regular basis in PL/SQL, you are really missing out.

Use this article as starting point for accessing a number of useful resources for getting up to speed on collections, and putting them to use in your programs.

Documentation

The PL/SQL User Guide offers detailed coverage of collection features here. It starts by reviewing the differences between collections types.

Articles

ORACLE-BASE: Collections in PL/SQL - a roundup of collection features by Tim Hall, with lots of coverage of MULTISET operators (set operations in PL/SQL, not SQL)

Multi-level collections in Oracle - great article by Adrian Billington on this advanced feature of collections (also known as nested collections)

New to 18c: Qualified expressions for associative array: it's just one new feature for collections, but it's a great one - essentially constructor functions for this type of collection. Plus I wanted to show you that even this "late in the game" as 18c, we are still enhancing collection functionality.

LiveSQL Scripts

LiveSQL offers 24x7 access to the latest version of Oracle Database. You can "play around" with SQL and PL/SQL in a scratchpad environment. It also offers a code library. There are literally dozens of scripts in that library that focus on various aspects of collections. Start here and then tune your search accordingly.

Videos

Playlist: Collections in PL/SQL

An 11-video Youtube playlist on my Practically Perfect PL/SQL channel. Just to give you a sense of the depth of coverage, total time is over 4.5 hours.

Playlist by Manish Sharma: PL/SQL Collections in Oracle Database

Manish (aka, Rebellion Rider) is one of the most prolific publishers of videos on Oracle PL/SQL. Check out this 17 video playlist for fast, basic videos on various aspects of collections.

Comments

Why DBMS_OUTPUT.PUT_LINE should not be in your application code

A database developer recently came across my Bulletproof PL/SQL presentation, which includes this slide. That first item in the list caught his attention: Never put calls to DBMS_OUTPUT.PUT_LINE in your application code. So he sent me an email asking why I would say that. Well, I suppose that is the problem with publishing slide decks. All the explanatory verbiage is missing. I suppose maybe I should do a video. :-) But in the meantime, allow me to explain. First, what does DBMS_OUTPUT.PUT_LINE do? It writes text out to a buffer, and when your current PL/SQL block terminates, the buffer is displayed on your screen. [Note: there can be more to it than that. For example, you could in your own code call DBMS_OUTPUT.GET_LINE(S) to get the contents of the buffer and do something with it, but I will keep things simple right now.] Second, if I am telling you not to use this built-in, how could text from your program be displayed on your screen? Not without a lot o...

How to Pick the Limit for BULK COLLECT

This question rolled into my In Box today: In the case of using the LIMIT clause of BULK COLLECT, how do we decide what value to use for the limit? First I give the quick answer, then I provide support for that answer Quick Answer Start with 100. That's the default (and only) setting for cursor FOR loop optimizations. It offers a sweet spot of improved performance over row-by-row and not-too-much PGA memory consumption. Test to see if that's fast enough (likely will be for many cases). If not, try higher values until you reach the performance level you need - and you are not consuming too much PGA memory. Don't hard-code the limit value: make it a parameter to your subprogram or a constant in a package specification. Don't put anything in the collection you don't need. [from Giulio Dottorini] Remember: each session that runs this code will use that amount of memory. Background When you use BULK COLLECT, you retrieve more than row with each fetch, ...

Recommendations for unit testing PL/SQL programs

I have recently received a couple of requests for recommendations regarding unit testing of PL/SQL programs. I thought I would share with you what I told them. First, some background: unit testing refers to the process of testing individual subprograms for correctness, as opposed to overall application testing (which, these days, almost always means visiting a website). The basic idea behind unit testing is that if you verify that each individual subprogram works correctly, then you are much less likely to have bugs in higher-level programs that call those tested subprograms. And when you do, you know you can focus on the way the tested subprograms are used, and not the subprograms themselves. The most important application of a unit test is to participate in a regression test , which can be run to verify one's code works today as well as it did yesterday. That will greatly reduce the chance of you upgrading the application and users complaining that a bunch of feature...

Obsessed with Oracle PL/SQL

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