Currently, pollutants are measured at different stations in a city and that data is aggregated to a single number (the air quality index) and published once a day on a website.

目前，污染物测量是在一个城市的多个不同地点进行测量的，然后数据会合计成一个数字(空气质量指数)最后在网站上每天发布一次。

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To use each variable, you simply use the column number as the index of the single value you want.

要使用每个变量，您只需将列号用作您所需值的索引即可。

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Number of index searches. Index searches are used to start range scans, single index record fetches, and to reposition within an index.

索引搜索的数目。索引搜索用于启动范围扫描和单个索引记录提取以及在索引中改变位置。

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