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摘要： SQL JOIN 连接 INNER JOIN 选择两个表中具有匹配值的记录（SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate FROM Orders INNER JOIN Customers ON Orders.Custo 阅读全文

摘要： 常用函数 AVG() - 返回平均值（SELECT AVG(column_name) FROM table_name WHERE condition;）COUNT() - 返回行数（SELECT COUNT(1) FROM table_name WHERE condition;）MAX() - 返回 阅读全文