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张小明 2026/1/5 19:05:52
珠海网站建设模板,东莞企业怎么做网站建设,网站建设服务器在国外如何打击,专业的内蒙古网站建设SQL 联查#xff08;Join#xff09;是将来自两个或多个表的数据结合在一起的操作。以下是一些常用的 SQL 联查示例#xff0c;包括内联接、左联接、右联接和全外联接。示例数据库表和数据1. Customers (客户表)CustomerIDNameCity1AliceNew York2BobLos Angeles3CharlieChi…SQL 联查Join是将来自两个或多个表的数据结合在一起的操作。以下是一些常用的 SQL 联查示例包括内联接、左联接、右联接和全外联接。示例数据库表和数据1. Customers (客户表)CustomerIDNameCity1AliceNew York2BobLos Angeles3CharlieChicago4DavidSan Francisco5EveMiami2. Orders (订单表)OrderIDCustomerIDOrderDateAmount10112025-01-15150.0010212025-02-20200.0010322025-01-25300.0010432025-03-05450.0010542025-04-10500.00查询和输出效果1. 内联接 (INNER JOIN)查询所有下过订单的客户及其订单信息SELECT Customers.CustomerID, Customers.Name, Orders.OrderID, Orders.OrderDate, Orders.Amount FROM Customers INNER JOIN Orders ON Customers.CustomerID Orders.CustomerID;输出结果CustomerIDNameOrderIDOrderDateAmount1Alice1012025-01-15150.001Alice1022025-02-20200.002Bob1032025-01-25300.003Charlie1042025-03-05450.004David1052025-04-10500.002. 左联接 (LEFT JOIN)查询所有客户及其订单信息包括没有下过订单的客户SELECT Customers.CustomerID, Customers.Name, Orders.OrderID, Orders.OrderDate, Orders.Amount FROM Customers LEFT JOIN Orders ON Customers.CustomerID Orders.CustomerID;输出结果CustomerIDNameOrderIDOrderDateAmount1Alice1012025-01-15150.001Alice1022025-02-20200.002Bob1032025-01-25300.003Charlie1042025-03-05450.004David1052025-04-10500.005EveNULLNULLNULL3. 右联接 (RIGHT JOIN)查询所有订单及其客户信息包括没有客户信息的订单SELECT Customers.CustomerID, Customers.Name, Orders.OrderID, Orders.OrderDate, Orders.Amount FROM Customers RIGHT JOIN Orders ON Customers.CustomerID Orders.CustomerID;输出结果CustomerIDNameOrderIDOrderDateAmount1Alice1012025-01-15150.001Alice1022025-02-20200.002Bob1032025-01-25300.003Charlie1042025-03-05450.004David1052025-04-10500.004. 全外联接 (FULL OUTER JOIN)查询所有客户与所有订单的信息包括没有匹配的客户和订单SELECT Customers.CustomerID, Customers.Name, Orders.OrderID, Orders.OrderDate, Orders.Amount FROM Customers FULL OUTER JOIN Orders ON Customers.CustomerID Orders.CustomerID;输出结果CustomerIDNameOrderIDOrderDateAmount1Alice1012025-01-15150.001Alice1022025-02-20200.002Bob1032025-01-25300.003Charlie1042025-03-05450.004David1052025-04-10500.005EveNULLNULLNULL