SQL FOREIGN KEY Constraint on CREATE TABLE

SQL FOREIGN KEY Constraint on CREATE TABLE
下面的 SQL 在 "Orders" 表创建时为 "Id_P" 列创建 FOREIGN KEY：

MySQL:
CREATE TABLE Orders
(
Id_O int NOT NULL,
OrderNo int NOT NULL,
Id_P int,
PRIMARY KEY (Id_O),
FOREIGN KEY (Id_P) REFERENCES Persons(Id_P)
)
SQL Server / Oracle / MS Access:
CREATE TABLE Orders
(
Id_O int NOT NULL PRIMARY KEY,
OrderNo int NOT NULL,
Id_P int FOREIGN KEY REFERENCES Persons(Id_P)
)