COUNT(id)与COUNT(*)在MySQL [英] COUNT(id) vs. COUNT(*) in MySQL
本文介绍了COUNT(id)与COUNT(*)在MySQL的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
假设表中有一个主要字段id(如速度等),以下查询之间是否有区别?
Is there a difference between the following queries, assuming there is a primary field 'id' in the table (as in speed, etc)?
SELECT COUNT(id)
FROM table
vs。
SELECT COUNT(*)
FROM table
推荐答案
查看 Count(*)vs Count(col)在www.mysqlperformanceblog.com,他们讨论这个主题的各种col类型(NOT NULL或不,索引等),这是MyISAM和InnoDB表。
Have a look at Count(*) vs Count(col) at www.mysqlperformanceblog.com, they discuss this topic for various 'col' types (NOT NULL or not, with index, etc) and this for MyISAM and InnoDB tables.
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