资格与拥有之间的区别

Question

谁能解释一下，Teradata 中的 qualify...over...partition by 和 group by...having 有什么区别？
我也想知道它们的性能是否有差异。

Answer 1

QUALIFY 是专有扩展，用于过滤 窗口聚合函数 .

的结果

查询按特定顺序进行逻辑处理：

FROM: 创建基本结果集
WHERE: 从之前的结果集中删除行
GROUP BY：对之前的结果集应用聚合函数
HAVING: 从先前的结果集中删除行
OVER: 对之前的结果集应用窗口聚合函数
QUALIFY：从之前的结果集中删除行

Answer 2

Having clause is used to filter the result set of the aggregate functions like (COUNT,min,max etc)
they eliminate rows based from groups based on some criteria like this :-
SELECT dept_no, MIN(salary), MAX(salary), AVG(salary)
     FROM employee
     WHERE dept_no IN (100,300,500,600)
     GROUP BY dept_no
     HAVING AVG(salary) > 37000;

The QUALIFY clause eliminates rows based on the function value, returning a new value for each of the participating rows.
It works on the final result set.

SELECT NAME,LOCATION FROM EMPLOYEE
 QUALIFY ROW_NUMBER() OVER ( PARTITION BY NAME ORDER BY JOINING_DATE DESC) = 1;


We can club both having and qualify as well in a query if we use both aggregate and analytical fucntion like below:-
SELECT StoreID, SUM(sale),
   SUM(profit) OVER (PARTITION BY StoreID)
   FROM facts
   GROUP BY StoreID, sale, profit
   HAVING SUM(sale) > 15
   QUALIFY SUM(profit) OVER (PARTITION BY StoreID) > 2;   



You can see there order of execution from dnoeth answer.

资格与拥有之间的区别

Difference between Qualify and Having

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