SQL 视图 - 如果为空，则添加默认值

SQL 视图 - 如果为空，则添加默认值？

sql
-- 创建一个名为 customers 的表
CREATE TABLE customers (
  id INT PRIMARY KEY,
  name VARCHAR(100),
  email VARCHAR(100)
);
-- 向 customers 表中插入一些数据
INSERT INTO customers (id, name, email)
VALUES (1, 'John Doe', 'john@example.com'),
       (2, 'Jane Smith', 'jane@example.com');
-- 创建一个名为 customers_view 的视图
CREATE VIEW customers_view AS
SELECT id, name, email
FROM customers
WHERE name LIKE 'John%';
-- 查询 customers_view 视图的结果
SELECT *
FROM customers_view;
-- 如果视图结果集为空，则返回默认值
SELECT 
  CASE WHEN COUNT(*) = 0 THEN 'No customers found' ELSE id END AS id,
  CASE WHEN COUNT(*) = 0 THEN 'No customers found' ELSE name END AS name,
  CASE WHEN COUNT(*) = 0 THEN 'No customers found' ELSE email END AS email
FROM customers_view;