《MySQL必知必会》第十七章-组合查询

原创于 2018-01-20 12:09:08 发布 · 176 阅读

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本文介绍如何使用SQL的UNION操作符来合并多个SELECT语句的结果集，并探讨UNION与UNION ALL的区别。此外，还展示了如何对组合后的查询结果进行排序。

使用UNION：
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_state IN ('IL', 'IN', 'MI')
UNION
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_name = 'Fun4All';

SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_state IN ('IL', 'IN', 'MI')
UNION ALL
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_name = 'Fun4All';

对组合查询结果排序：
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_state IN ('IL', 'IN', 'MI')
UNION
SELECT cust_name, cust_contact, cust_email
FROM Customers
WHERE cust_name = 'Fun4All'
ORDER BY cust_name, cust_contact;