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    mysql raw data
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    没有where的count()使用MyISAM要比InnoDB快得多。因为MyISAM内置了一个计数器,count()时它直接从计数器中读,而InnoDB必须扫描全表。所以在InnoDB上执行count()时一般要伴随where,且where中要包含主键以外的索引列。为什么这里特别强调“主键以外”?因为InnoDB中primary index是和raw data存放在一起的,而secondary index则是单独存放,然后有个指针指向primary key。所以只是count()的话使用secondary index扫描更快,而primary key则主要在扫描索引同时要返回raw data时的作用较大。

    这里的raw data 怎么理解

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    • 只是入戏太深 普通会员 1楼

      MySQL raw data is raw data that is stored in the MySQL server without any transformation or formatting. Raw data is typically used to store data that is not properly formatted or that requires special handling before it can be used in a database query. Raw data is often used in conjunction with the built-in functions in MySQL to perform data transformations or to format data for display in reports. Raw data is typically stored in a binary format, which is not easily readable or editable by humans. The structure of raw data can vary depending on the specific use case. For example, raw data may be stored in a binary file format, such as a file with one row per line, or in a comma-separated value (CSV) format, which allows for easy import and export of data. Additionally, raw data may be stored in a specific format, such as JSON or XML, which is more human-readable and can be easily processed by software programs. It's worth noting that raw data is not a reliable or secure way to store data, as it is vulnerable to unauthorized access or manipulation. Therefore, it's important to ensure that raw data is properly secured and that it is only used for authorized purposes.

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