clickhouse where having
时间: 2023-08-15 17:12:51 浏览: 38
`HAVING` clause is used in ClickHouse to filter the results of a `GROUP BY` query. It allows you to specify a condition that is applied after grouping has been done. The syntax for using `HAVING` clause in ClickHouse is as follows:
```
SELECT column1, column2, aggregate_function(column3)
FROM table_name
WHERE condition
GROUP BY column1, column2
HAVING condition
```
Here, the `WHERE` clause is used to filter the rows before grouping, while the `HAVING` clause is used to filter the groups after grouping. The `HAVING` clause can contain any valid expression, including aggregate functions, and can be used to specify conditions such as minimum, maximum, or average values of grouped data.
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where 和having
where和having是SQL语句中用于筛选数据的关键字,它们有以下几个区别:
1. where是一个约束声明,用于在查询返回结果之前对数据进行筛选,而having是一个过滤声明,用于在查询返回结果之后对结果集进行过滤。\[1\]
2. where可以直接使用表中的字段作为筛选条件,但不能使用分组中的计算函数作为筛选条件;而having必须与group by配合使用,可以使用分组计算的函数和分组字段作为筛选条件。\[2\]
3. 在执行顺序上,where子句在聚合前先筛选记录,作用在group by子句和having子句前;而having子句在聚合后对组记录进行筛选。\[1\]
4. where不能使用聚合函数,而having可以使用聚合函数。\[1\]
总结起来,where用于在查询之前对数据进行筛选,而having用于在查询结果返回之后对结果集进行过滤。where可以直接使用表中的字段作为筛选条件,而having必须与group by配合使用,并可以使用分组计算的函数和分组字段作为筛选条件。\[1\]\[2\]
#### 引用[.reference_title]
- *1* [SQL中where与having的区别](https://blog.csdn.net/yajie_china/article/details/80089553)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insertT0,239^v3^insert_chatgpt"}} ] [.reference_item]
- *2* [【Where和having的区别】条件语句where和having有什么不同?](https://blog.csdn.net/qq_43555403/article/details/123198203)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insertT0,239^v3^insert_chatgpt"}} ] [.reference_item]
- *3* [where、having的区别和用法](https://blog.csdn.net/ws_Ando/article/details/86612414)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insertT0,239^v3^insert_chatgpt"}} ] [.reference_item]
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where和having
Where是一个SQL语句中的关键词,用于指定查询结果集的限制条件,即指定需要查询的列或行所满足的条件。例如,SELECT * FROM table_name WHERE column_name = 'value';这个查询语句将从表中选择列名为column_name,并且其对应的值为'value'的行。
Having也是一个SQL语句中的关键词,用于在对查询结果进行分组聚合操作(例如COUNT, SUM, AVG等)之后,过滤掉一部分结果。它可以用于在GROUP BY子句之后加入筛选条件。例如,SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name HAVING COUNT(*) > 10;这个查询将从表中选择列名为column_name,并使用GROUP BY统计每种不同的值出现的次数,然后使用HAVING过滤出统计次数大于10的结果。