sql自学记录

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SQL join ：用于根据两个或多个表中的列之间的关系，从这些表中查询数据

eg:

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons, Orders
WHERE Persons.Id_P = Orders.Id_P

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
INNER JOIN Orders
ON Persons.Id_P = Orders.Id_P
ORDER BY Persons.LastName

外连接

LEFT JOIN 关键字语法

SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name

SQL FULL JOIN 关键字

只要其中某个表存在匹配，FULL JOIN 关键字就会返回行。

SELECT column_name(s)
FROM table_name1
FULL JOIN table_name2
ON table_name1.column_name=table_name2.column_name

数据库系统原理(二) - SunArmy - 博客园 (cnblogs.com)