SQL GROUP BY and HAVING

最新推荐文章于 2025-06-15 15:23:07 发布

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最新推荐文章于 2025-06-15 15:23:07 发布

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本文链接：https://blog.youkuaiyun.com/toyijiu/article/details/90720267

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博客介绍了GROUP BY和HAVING子句。GROUP BY可将SUM和COUNT等函数应用于共享值的项组，指定GROUP BY continent时，每个不同的continent值仅返回一行，其他列需用SUM、COUNT等聚合。HAVING用于过滤显示的组，WHERE在聚合前过滤行，HAVING在聚合后过滤。还提到ORDER BY可按列位置引用。

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GROUP BY and HAVING

By including a GROUP BY clause functions such as SUM and COUNT are applied to groups of items sharing values. When you specify GROUP BY continent the result is that you get only one row for each different value of continent. All the other columns must be “aggregated” by one of SUM, COUNT …

The HAVING clause allows use to filter the groups which are displayed. The WHERE clause filters rows before the aggregation, the HAVING clause filters after the aggregation.

If a ORDER BY clause is included we can refer to columns by their position.