UNION SELECTs-循环?或单个查询? [英] UNION SELECTs - loop? or single query?

问题描述

如果我使用UNION从数据库中进行多个SELECT，是否被视为一个查询?或多个查询?

If I use UNION to make multiple SELECTs from database, is considered one query? or multiple queries?

SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;

这是否被视为单个查询?或2个查询?

Is this considered a single query? or 2 queries?

(每小时的查询数量有限，我想优化我的代码)

(I am limited at number of queries per hour and I wan to optimise my code)

谢谢！

推荐答案

来自文档:

SQL UNION运算符用于合并2个或更多的结果集 SELECT语句.它删除了各行之间的重复行 SELECT语句.

The SQL UNION operator is used to combine the result sets of 2 or more SELECT statements. It removes duplicate rows between the various SELECT statements.

因此，您的2个选择将合并为一个查询;)

So your 2 select are combined into one query ;)

http://www.techonthenet.com/sql/union.php

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