Skip to main content

12.2: Avoid hard-coding maximum length of VARCHAR2 (and more)

Starting with Oracle Database 12c Release 2 (12.2), we can now use static expressions* where previously only literal constants were allowed. Here are some examples (also available in this LiveSQL script):


CREATE OR REPLACE PACKAGE pkg
   AUTHID DEFINER
IS
   c_max_length constant integer := 32767;
   SUBTYPE maxvarchar2 IS VARCHAR2 (c_max_length);
END;   
/

DECLARE
   l_big_string1 VARCHAR2 (pkg.c_max_length) := 'So big....';
   l_big_String2 pkg.maxvarchar2 := 'So big via packaged subtype....';
   l_half_big VARCHAR2 (pkg.c_max_length / 2) := 'So big....';
BEGIN   
   DBMS_OUTPUT.PUT_LINE (l_big_string1);
   DBMS_OUTPUT.PUT_LINE (l_big_string2);
END;
/

As you can see from this code, static expressions can now be used in subtype declarations.

The definition of static expressions is expanded to include all the PL/SQL scalar types and a much wider range of operators. Character operands are restricted to a safe subset of the ASCII character set. Operators whose results depend on any implicit NLS parameter are disallowed

Expanded and generalized expressions have two primary benefits for PL/SQL developers:
  • Programs are much more adaptable to changes in their environment
  • Programs are more compact, clearer, and substantially easier to understand and maintain
* A static expression is an expression whose value can be determined at compile time. This means the expression cannot include character comparisons, variables, or function invocations. An expression is static if it is any of the following:
  • the NULL literal
  • a character, numeric, or boolean literal
  • a reference to a static constant
  • a reference to a conditional compilation variable begun with $$ 
  • an operator is allowed in static expressions, if all of its operands are static, and if the operator does not raise an exception when it is evaluated on those operands
Read more in the doc

Comments

Popular posts from this blog

Quick Guide to User-Defined Types in Oracle PL/SQL

A Twitter follower recently asked for more information on user-defined types in the PL/SQL language, and I figured the best way to answer is to offer up this blog post. PL/SQL is a strongly-typed language . Before you can work with a variable or constant, it must be declared with a type (yes, PL/SQL also supports lots of implicit conversions from one type to another, but still, everything must be declared with a type). PL/SQL offers a wide array of pre-defined data types , both in the language natively (such as VARCHAR2, PLS_INTEGER, BOOLEAN, etc.) and in a variety of supplied packages (e.g., the NUMBER_TABLE collection type in the DBMS_SQL package). Data types in PL/SQL can be scalars, such as strings and numbers, or composite (consisting of one or more scalars), such as record types, collection types and object types. You can't really declare your own "user-defined" scalars, though you can define subtypes  from those scalars, which can be very helpful from the p

The differences between deterministic and result cache features

 EVERY once in a while, a developer gets in touch with a question like this: I am confused about the exact difference between deterministic and result_cache. Do they have different application use cases? I have used deterministic feature in many functions which retrieve data from some lookup tables. Is it essential to replace these 'deterministic' key words with 'result_cache'?  So I thought I'd write a post about the differences between these two features. But first, let's make sure we all understand what it means for a function to be  deterministic. From Wikipedia : In computer science, a deterministic algorithm is an algorithm which, given a particular input, will always produce the same output, with the underlying machine always passing through the same sequence of states.  Another way of putting this is that a deterministic subprogram (procedure or function) has no side-effects. If you pass a certain set of arguments for the parameters, you will always get

My two favorite APEX 5 features: Regional Display Selector and Cards

We (the over-sized development team for the PL/SQL Challenge - myself and my son, Eli) have been busy creating a new website on top of the PLCH platform (tables and packages): The Oracle Dev Gym! In a few short months (and just a part time involvement by yours truly), we have leveraged Oracle Application Express 5 to create what I think is an elegant, easy-to-use site that our users will absolutely love.  We plan to initially make the Dev Gym available only for current users of PL/SQL Challenge, so we can get feedback from our loyal user base. We will make the necessary adjustments and then offer it for general availability later this year. Anyway, more on that as the date approaches (the date being June 27, the APEX Open Mic Night at Kscope16 , where I will present it to a packed room of APEX experts). What I want to talk about today are two features of APEX that are making me so happy these days: Regional Display Selector and Cards. Regional Display Sel