SELECT funcionario.name WHERE COUNT（）> AVG（）GROUP BY funcionario

Question

我不會給選擇funcionario.name WHERE COUNT（）> AVG（）GROUP BY funcionario

funcionario =僱員

cliente =客戶端

SELECT funcionario.nome 
FROM cliente 
INNER JOIN funcionario ON cliente.nr_funcionario = funcionario.nr_funcionario 
WHERE 
((SELECT COUNT(*) 
    FROM cliente 
    INNER JOIN funcionario ON cliente.nr_funcionario = funcionario.nr_funcionario 
    GROUP BY funcionario.nome) > 
(SELECT AVG(total) 
FROM 
    (SELECT COUNT(*) AS total 
    FROM cliente 
    INNER JOIN funcionario ON cliente.nr_funcionario = funcionario.nr_funcionario 
    GROUP BY funcionario.nome))) 
GROUP BY funcionario.nome 

Answer 1

我得到你感到困惑如何在查詢中放置一個約束在一個給定的組感。 HAVING關鍵字用於此目的，可以認爲這是WHERE子句對單個記錄做的事情，除了它代替組記錄的行爲。然而，使用公共表表達式，可以大大簡化查詢到以下幾點：

WITH cte AS (
    SELECT f.nome, COUNT(*) AS total 
    FROM cliente c 
    INNER JOIN funcionario 
     ON c.nr_funcionario = f.nr_funcionario 
    GROUP BY f.nome 
) 
SELECT t.nome 
FROM cte t 
WHERE t.total > (SELECT AVG(total) FROM cte) 

Answer 2

由於我沒有實際的表來測試， 而是使用了以下概念，你一定會得到正確的結果

declare @average int; 
    SELECT @average= AVG(count (*)) 
    FROM 
     FROM cliente 
     INNER JOIN funcionario ON cliente.nr_funcionario = funcionario.nr_funcionario 
     GROUP BY funcionario.nome 


     SELECT funcionario.nome 
    FROM cliente 
    INNER JOIN funcionario ON cliente.nr_funcionario = funcionario.nr_funcionario 
     GROUP BY funcionario.nome 
having count(functionario.nome)>@average 

Answer 3

我認爲最好的辦法是使用窗口功能：

select nome 
from (select f.nome, count(*) AS total, 
      avg(count(*) * 1.0) over() as avg_total 
     from cliente c join 
      funcionario f 
      on c.nr_funcionario = f.nr_funcionario 
     group by f.nome 
    ) fc 
where total > avg_total; 

這應該比引用CTE版本更好的性能不止一次。