spread默认值是多少？

`newpnn` 函数中的 `spread` 参数没有默认值，它必须由用户指定。`spread` 参数控制最近邻居的影响范围，它越大，最近邻居对输出结果的影响就越大。通常情况下，`spread` 的值需要经过调试才能确定。一般来说，`spread` 的取值范围是 0 到 1 之间的实数，一般情况下，较小的 `spread` 值可以提高 PNN 的准确率，但如果 `spread` 值太小，可能会导致过拟合。最佳的 `spread` 值需要结合具体的问题和数据集来进行调整。

相关问题

qt 渐变qlineargradient spread

Qt中的QLinearGradient渐变可以通过spread方法来控制渐变的填充方式。spread方法有三种取值：

1. PadSpread：默认值，表示在渐变范围之外的区域填充最近的渐变颜色。

2. RepeatSpread：表示在渐变范围之外的区域填充重复的渐变颜色。

3. ReflectSpread：表示在渐变范围之外的区域填充反射的渐变颜色。

例如，如果在QLinearGradient对象中使用spread方法设置为RepeatSpread，则在渐变范围之外的区域将会以重复的方式填充渐变颜色，直到填满整个区域。

所有要求都是用sql sever语句实现 创建一个数据库，至少里面有5个表，没个表至少有十条数据，至少有俩个表具有外键 使用模式匹配查询，使用top查询，in查询，降序查询，使用count集合函数查询，分组统计查询，使用连接条件的多表查询，比较运算符的子查询，使用in的子查询 创建视图并使用 ;创建索引; 创建唯一性约束，检查约束，默认值约束，外键约束; 创建一个存储过程并使用 ;在某个表上创建一个插入和更新的dml触发器

好的，我会根据您的要求来回答问题。以下是针对您的问题的答案：

1. 创建数据库并添加表和数据：

CREATE DATABASE MyDatabase;

USE MyDatabase;

CREATE TABLE Customers (
  CustomerID INT PRIMARY KEY,
  CustomerName VARCHAR(50),
  ContactName VARCHAR(50),
  Country VARCHAR(50)
);

CREATE TABLE Orders (
  OrderID INT PRIMARY KEY,
  CustomerID INT,
  OrderDate DATE,
  ShipCity VARCHAR(50),
  FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

CREATE TABLE Products (
  ProductID INT PRIMARY KEY,
  ProductName VARCHAR(50),
  SupplierID INT,
  CategoryID INT,
  Price DECIMAL(10,2),
  FOREIGN KEY (SupplierID) REFERENCES Suppliers(SupplierID),
  FOREIGN KEY (CategoryID) REFERENCES Categories(CategoryID)
);

CREATE TABLE Suppliers (
  SupplierID INT PRIMARY KEY,
  SupplierName VARCHAR(50),
  ContactName VARCHAR(50),
  Country VARCHAR(50)
);

CREATE TABLE Categories (
  CategoryID INT PRIMARY KEY,
  CategoryName VARCHAR(50),
  Description VARCHAR(500)
);

INSERT INTO Customers VALUES (1, 'Alfreds Futterkiste', 'Maria Anders', 'Germany');
INSERT INTO Customers VALUES (2, 'Ana Trujillo Emparedados', 'Ana Trujillo', 'Mexico');
INSERT INTO Customers VALUES (3, 'Antonio Moreno Taquería', 'Antonio Moreno', 'Mexico');
INSERT INTO Customers VALUES (4, 'Around the Horn', 'Thomas Hardy', 'UK');
INSERT INTO Customers VALUES (5, 'Berglunds snabbköp', 'Christina Berglund', 'Sweden');
INSERT INTO Customers VALUES (6, 'Blauer See Delikatessen', 'Hanna Moos', 'Germany');
INSERT INTO Customers VALUES (7, 'Blondel père et fils', 'Frédérique Citeaux', 'France');
INSERT INTO Customers VALUES (8, 'Bólido Comidas preparadas', 'Martín Sommer', 'Spain');
INSERT INTO Customers VALUES (9, 'Bon app', 'Laurence Lebihans', 'France');
INSERT INTO Customers VALUES (10, 'Bottom-Dollar Markets', 'Elizabeth Lincoln', 'Canada');

INSERT INTO Orders VALUES (1, 1, '2021-01-01', 'Berlin');
INSERT INTO Orders VALUES (2, 2, '2021-01-02', 'Mexico City');
INSERT INTO Orders VALUES (3, 2, '2021-01-03', 'Mexico City');
INSERT INTO Orders VALUES (4, 3, '2021-01-04', 'Mexico City');
INSERT INTO Orders VALUES (5, 3, '2021-01-05', 'Mexico City');
INSERT INTO Orders VALUES (6, 3, '2021-01-06', 'Mexico City');
INSERT INTO Orders VALUES (7, 4, '2021-01-07', 'London');
INSERT INTO Orders VALUES (8, 5, '2021-01-08', 'Stockholm');
INSERT INTO Orders VALUES (9, 6, '2021-01-09', 'Munich');
INSERT INTO Orders VALUES (10, 7, '2021-01-10', 'Paris');

INSERT INTO Products VALUES (1, 'Chai', 1, 1, 18.00);
INSERT INTO Products VALUES (2, 'Chang', 1, 1, 19.00);
INSERT INTO Products VALUES (3, 'Aniseed Syrup', 1, 2, 10.00);
INSERT INTO Products VALUES (4, 'Chef Anton''s Cajun Seasoning', 2, 2, 22.00);
INSERT INTO Products VALUES (5, 'Chef Anton''s Gumbo Mix', 2, 2, 21.35);
INSERT INTO Products VALUES (6, 'Grandma''s Boysenberry Spread', 3, 2, 25.00);
INSERT INTO Products VALUES (7, 'Uncle Bob''s Organic Dried Pears', 3, 7, 30.00);
INSERT INTO Products VALUES (8, 'Northwoods Cranberry Sauce', 3, 2, 40.00);
INSERT INTO Products VALUES (9, 'Mishi Kobe Niku', 4, 6, 97.00);
INSERT INTO Products VALUES (10, 'Ikura', 4, 8, 31.00);

INSERT INTO Suppliers VALUES (1, 'Exotic Liquids', 'Charlotte Cooper', 'UK');
INSERT INTO Suppliers VALUES (2, 'New Orleans Cajun Delights', 'Shelley Burke', 'USA');
INSERT INTO Suppliers VALUES (3, 'Grandma Kelly''s Homestead', 'Regina Murphy', 'USA');
INSERT INTO Suppliers VALUES (4, 'Tokyo Traders', 'Yoshi Nagase', 'Japan');
INSERT INTO Suppliers VALUES (5, 'Cooperativa de Quesos ''Las Cabras''', 'Antonio del Valle Saavedra', 'Spain');

INSERT INTO Categories VALUES (1, 'Beverages', 'Soft drinks, coffees, teas, beers, and ales');
INSERT INTO Categories VALUES (2, 'Condiments', 'Sweet and savory sauces, relishes, spreads, and seasonings');
INSERT INTO Categories VALUES (3, 'Confections', 'Desserts, candies, and sweet breads');
INSERT INTO Categories VALUES (4, 'Dairy Products', 'Cheeses');
INSERT INTO Categories VALUES (5, 'Grains/Cereals', 'Breads, crackers, pasta, and cereal');
INSERT INTO Categories VALUES (6, 'Meat/Poultry', 'Prepared meats');
INSERT INTO Categories VALUES (7, 'Produce', 'Dried fruit and bean curd');
INSERT INTO Categories VALUES (8, 'Seafood', 'Seaweed and fish');

2. 使用不同的查询：

使用模式匹配查询：

SELECT * FROM Customers WHERE CustomerName LIKE '%a%';

使用TOP查询：

SELECT TOP 5 * FROM Customers ORDER BY CustomerID;

使用IN查询：

SELECT * FROM Customers WHERE Country IN ('Germany', 'Mexico');

降序查询：

SELECT * FROM Customers ORDER BY CustomerName DESC;

使用COUNT集合函数查询：

SELECT COUNT(*) FROM Customers;

分组统计查询：

SELECT Country, COUNT(*) FROM Customers GROUP BY Country;

使用连接条件的多表查询：

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

比较运算符的子查询：

SELECT * FROM Customers WHERE CustomerID IN (SELECT CustomerID FROM Orders);

使用IN的子查询：

SELECT * FROM Customers WHERE Country IN (SELECT Country FROM Customers WHERE CustomerName = 'Alfreds Futterkiste');

3. 创建视图：

CREATE VIEW OrderDetails AS
SELECT Customers.CustomerName, Orders.OrderDate, Products.ProductName, Products.Price
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN OrderDetails ON OrderDetails.OrderID = Orders.OrderID)
INNER JOIN Products ON OrderDetails.ProductID = Products.ProductID;

4. 创建索引：

CREATE INDEX idx_CustomerName ON Customers (CustomerName);

5. 创建唯一性约束，检查约束，默认值约束，外键约束：

ALTER TABLE Customers
ADD CONSTRAINT uc_CustomerName UNIQUE (CustomerName);

ALTER TABLE Customers
ADD CONSTRAINT chk_Country CHECK (Country IN ('USA', 'UK', 'Mexico', 'Germany', 'France', 'Spain', 'Sweden'));

ALTER TABLE Customers
ADD CONSTRAINT df_ContactName DEFAULT 'N/A' FOR ContactName;

ALTER TABLE Orders
ADD CONSTRAINT fk_CustomerID FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID);

6. 创建存储过程：

CREATE PROCEDURE GetOrdersByCustomer
  @CustomerID INT
AS
BEGIN
  SELECT * FROM Orders WHERE CustomerID = @CustomerID;
END;

7. 创建触发器：

CREATE TRIGGER tr_UpdateProductPrice
ON Products
FOR INSERT, UPDATE
AS
BEGIN
  UPDATE Products
  SET Price = Price * 1.1
  FROM inserted
  WHERE Products.ProductID = inserted.ProductID;
END;