PL/SQL 中的 IN、OUT、IN OUT 参数到底是什么
What exactly are IN, OUT, IN OUT parameters in PL/SQL
我已经在这里查过问题，也看过在线和观看视频，但我仍然对 IN、OUT 到底是什么感到困惑。我问的原因是因为我正在编写一个程序，该程序将根据其他程序中的 IN 参数记录错误，
干杯！
Oracle 文档 here 很好地解释了：
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).
以及关于OUT参数的具体：
... 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.
编辑
实际上，尽管上面提供的信息是有效的，但我链接到的资源很差（SQL*Ada 程序员指南模块）。
可以在此处找到更好、更完整的资源以更好地理解这 3 种模式：Table 8-1 PL/SQL Subprogram Parameter Modes。
IN模式:
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模式：
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 NULL except for a record type with a non-NULL default 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 as NOT NULL.
By default, actual parameter is passed by value; if you specify NOCOPY, it might be passed by reference.
IN OUT模式：
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.
我已经在这里查过问题，也看过在线和观看视频，但我仍然对 IN、OUT 到底是什么感到困惑。我问的原因是因为我正在编写一个程序，该程序将根据其他程序中的 IN 参数记录错误，
干杯！
Oracle 文档 here 很好地解释了：
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).
以及关于OUT参数的具体：
... 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.
编辑
实际上，尽管上面提供的信息是有效的，但我链接到的资源很差（SQL*Ada 程序员指南模块）。
可以在此处找到更好、更完整的资源以更好地理解这 3 种模式：Table 8-1 PL/SQL Subprogram Parameter Modes。
IN模式:
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模式：
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模式：
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.