How to define mysql union query

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Release: 2023-05-29 18:10:06
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1. Also called connection query, it connects data in multiple tables to obtain a result set. When one table cannot satisfy the query results, you need to use a union query.

2. Premise, there must be logical correlation between joint tables.

Example

-- 示例: select orders.order_id, orders.amt, customer.cust_name, customer.tel_no from orders, customer where orders.cust_id = customer.cust_id; -- 起别名 select a.order_id, a.amt, b.cust_name, b.tel_no from orders a, customer b where a.cust_id = b.cust_id;
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