If you include the NOT NULL constraint in the declaration, then you must provide an initial value (as with a constant, see below). For most data types, a variable declaration can also specify an initial value. You declare a variable when you need to manipulate it (set, change and use its value) in your block.Ī variable declaration always specifies the name and data type of the variable. Smart, tightly integrated database programming languages do a lot of fine work on our behalf! Check out my LiveSQL script for a demonstration of this wonderfulness. Not only do you avoid copying and hard-coding the datatype (most critically the maximum length of your VARCHAR2 string), but whenever the object to which you anchored changes, the program unit containing the anchoring will be marked INVALID and recompiled automatically by the PL/SQL engine.Īnd after that recompilation, the datatype for your declarations will be updated to match the underlying structure. If you need to declare a record with the same structure as an entire row in a table or view, go with %ROWTYPE: So if you need to declare a variable or constant with the same type as a (and usually to hold a value from) column in a table, you should literally declare it that way with the %TYPE anchor:Ĭ_hdate CONSTANT employees.hire_date%TYPE When you building code on top of your data structures, as you do with PL/SQL, pretty clearly your most important "point of definition" are those structures: tables and views. I also like to think of this more positively as SPOD: Single Point of Definition. I am deeply attached to the DRY principle: Don't Repeat Yourself. Suppose, for example, that I need to declare two integer variables. You can only define one variable or constant per declaration. Instead, you can defer declaring elements until they are needed (either within the nested block or inside a nested subprogram).Ģ. Notice that the nested block also means that you do not have to "front load" all declarations for a big procedure or function at the top. You can get a similar effect, with nested anonymous blocks, as in: Other languages let you declare variables anywhere, right when you need them. So to be clear: there is an explicit "DECLARE" section only for unnamed blocks. You can only have declarations in the declaration section, which is found between the IS | AS | DECLARE keyword and the BEGIN keyword (which kicks off the executable section) or END keyword if declaring elements at the package level. So I offer another post on PL/SQL fundamentals, this one offering key points to remember when declaring constants and variables.ġ. And then you also quickly see how powerful and capable is PL/SQL. It is easy to learn the basics of PL/SQL, and you can become productive very quickly. The "deception" lies in how simplicity can sometimes mask capability. PL/SQL is, in almost all ways, a straightforward and deceptively simple programming language.
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