Prentice Hall Oracle Plsql By Example 3Rd Edition [Electronic resources] نسخه متنی

Lab 12.2 Passing Parameters In and Out of Procedures

Parameters

Parameters are the means to pass values to and from the calling environment to the server. These are the values that will be processed or returned via the execution of the procedure. There are three types of parameters: IN, OUT, and IN OUT.

Modes

Modes specify whether the parameter passed is read in or a receptacle for what comes out.

Figure 12.1 illustrates the relationship between the parameters when they are in the procedure header versus when the procedure is executed.

Formal and Actual Parameters

Formal parameters are the names specified within parentheses as part of the header of a module. Actual parameters are the valuesexpressions specified within parentheses as a parameter listwhen a call is made to the module. The formal parameter and the related actual parameter must be of the same or compatible datatypes. Table 12.1 explains the three types of parameters.

Passing of Constraints (Datatype) with Parameter Values

Formal parameters do not require constraints in datatypefor example, instead of specifying a constraint such as VARCHAR2(60), you just say VARCHAR2 against the parameter name in the formal parameter list. The constraint is passed with the value when a call is made.

Matching Actual and Formal Parameters

Two methods can be used to match actual and formal parameters: positional notation and named notation. Positional notation is simply association by position: The order of the parameters used when executing the procedure matches the order in the procedure's header exactly. Named notation is explicit association using the symbol =>.

Table 12.1. Three Types of Parameters

Syntax: formal_parameter_name => argument_value

In named notation, the order does not matter. If you mix notation, list positional notation before named notation.

Default values can be used if a call to the program does not include a value in the parameter list. Note that it makes no difference which style is used; they will both function similarly.