MySQL D5

Inner Join 以foreign key为基准，只留下重合部分的数据

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

Left Join

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

Right Join

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

Full Join

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

注意：MySQL里没有Full Join语法，可以用Left Join＋Right Join代替。

Union

SELECT column_name(s) FROM table_name1 UNION / UNION ALL SELECT column_name(s) FROM table_name2 注： UNION 操作符选取不同的值，UNION ALL 允许重复的值。  

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练习

USE ClassicModels;

1. 找出customer支付的check number， 如果没有check number， 也要保留customer （提示：Customers.customerNumber, Payments.checkNumber）

2. 找出customer支付的check number， 如果没有check number，不用保留 customer （提示：Customers.customerNumber, Payments.checkNumber）

3. 找出order number 对应的所有product line， 如果没有匹配，order number和product line也都要保留 （提示：OrderDetails.orderNumber, Products.productLine）

USE ClassicModels;

## 找出customer支付的check number， 如果没有check number， 也要保留customer

## Customers.customerNumber, Payments.checkNumber

SELECT*FROM customers;

SELECT*FROM payments;

SELECT customers.customerNumber, payments.checkNumber

FROM customers LEFT JOIN payments ON customers.customerNumber=payments.customerNumber;

## 找出customer支付的check number， 如果没有check number，不用保留customer

## Customers.customerNumber, Payments.checkNumber

SELECT customers.customerNumber, payments.checkNumber

FROM customers Right JOIN payments ON customers.customerNumber=payments.customerNumber;

## 找出order number 对应的所有product line， 如果没有匹配，order number和product line也都要保留

## OrderDetails.orderNumber, Products.productLine

SELECT orderdetails.orderNumber, products.productLine

FROM orderdetails Left JOIN products ON orderdetails.productCode=products.productCode

UNION

SELECT orderdetails.orderNumber, products.productLine

FROM orderdetails Right JOIN products ON orderdetails.productCode=products.productCode;