sql - SQL 中 HAVING 和 WHERE 子句的区别

Question

这个问题在这里已经有了答案:





What is the difference between HAVING and WHERE in SQL?

(18 个回答)


8年前关闭。

SELECT column_name, aggregate_function(column_name) 
FROM table_name 
WHERE column_name operator value 
GROUP BY column_name 
HAVING aggregate_function(column_name) operator value

have 和 where 和有什么不一样

Answer 1

where select ... from 上的过滤器
having过滤来自 group by ... 的聚合结果

所以，再看看你的例子:

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value

在这里， WHERE column_name operator value说“返回 table_name 的结果，其中
‘column_name 运算符值’为真”。

只有在找到这些条件的所有结果后，它才会按 column_name 分组。

然后 HAVING aggregate_function(column_name) operator value说“对于生成的聚合组，运行 'aggregate_function(column_name)' 并仅返回 'aggregate_function(column_name) 运算符值'为真的结果。”