问题
I've looked up questions here as well as looking online and watching videos but I'm still confused exactly what IN, OUT is. The reason I'm asking is because I'm writing a procedure that will log an error based on the IN parameters in other procedures,
Cheers!
回答1:
The Oracle documentation here does a good job of explaining:
The mode of a parameter indicates whether the parameter passes data to a procedure (
IN), returns data from a procedure (OUT), or can do both (IN OUT).
And about OUT parameters specifically:
... you cannot use it to pass a value to the procedure. Nor can you read its value inside the procedure, even after a value has been assigned to it.
EDIT
Actually, though the information provided above is valid, I linked to a poor resource (SQL*Module for Ada Programmer's Guide).
A much better and more complete resource to better understand the 3 modes can be found here: Table 8-1 PL/SQL Subprogram Parameter Modes.
IN mode:
Default mode
Passes a value to the subprogram.
Formal parameter acts like a constant: When the subprogram begins, its value is that of either its actual parameter or default value, and the subprogram cannot change this value.
Actual parameter can be a constant, initialized variable, literal, or expression.
Actual parameter is passed by reference.
OUT mode:
Must be specified.
Returns a value to the invoker.
Formal parameter is initialized to the default value of its type. The default value of the type is
NULLexcept for a record type with a non-NULLdefault value.When the subprogram begins, the formal parameter has its initial value regardless of the value of its actual parameter. Oracle recommends that the subprogram assign a value to the formal parameter.
If the default value of the formal parameter type is
NULL, then the actual parameter must be a variable whose data type is not defined asNOT NULL.By default, actual parameter is passed by value; if you specify
NOCOPY, it might be passed by reference.
IN OUT mode:
Must be specified.
Passes an initial value to the subprogram and returns an updated value to the invoker.
Formal parameter acts like an initialized variable: When the subprogram begins, its value is that of its actual parameter. Oracle recommends that the subprogram update its value.
Actual parameter must be a variable (typically, it is a string buffer or numeric accumulator).
By default, actual parameter is passed by value (in both directions); if you specify
NOCOPY, it might be passed by reference.
来源：https://stackoverflow.com/questions/32634123/what-exactly-are-in-out-in-out-parameters-in-pl-sql