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codethereforam/mysql-count.md

Last active February 1, 2019 01:48
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mysql count(*) vs count(1)
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mysql-count.md

perfer count(*)

  1. 官方文档:

InnoDB handles SELECT COUNT(*) and SELECT COUNT(1) operations in the same way. There is no performance difference.

  1. 阿里手册：

【强制】不要使用 count( 列名 ) 或 count( 常量 ) 来替代 count( * ) ， count( * ) 是 SQL 92 定义的 标准统计行数的语法，跟数据库无关，跟 NULL 和非 NULL 无关。 说明： count( * ) 会统计值为 NULL 的行，而 count( 列名 ) 不会统计此列为 NULL 值的行。

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