Можете ли вы разделить один псевдоним на другой в MySQL?

Question

У меня запрос к нескольким таблицам, похожий на этот (упрощенная версия)

SELECT columns, count(table2.rev_id) As rev_count, sum(table2.rev_rating) As sum_rev_rating 
FROM table1
LEFT JOIN table2
ON table1.dom_id = table2.rev_domain_from 
WHERE dom_lastreview != 0 AND rev_status = 1 
GROUP BY dom_url 
ORDER BY sum_rev_rating/rev_count DESC

Проблема в предложении ORDER BY. Это приводит к ошибке MySQL, которая выглядит следующим образом:

Ссылка 'sum_ rev_ rating' не поддерживается (ссылка на групповую функцию)

Answer 1

Вы не можете делать вычисления с псевдонимами. Один из способов сделать это - просто создать другой псевдоним и порядок.

SELECT columns, count(table2.rev_id) As rev_count, sum(table2.rev_rating) As sum_rev_rating, sum(table2.rev_rating)/count(table2.rev_id) as avg_rev_rating
FROM table1
LEFT JOIN table2
ON table1.dom_id = table2.rev_domain_from 
WHERE dom_lastreview != 0 AND rev_status = 1 
GROUP BY dom_url 
ORDER BY avg_rev_rating DESC

Answer 2

мой mysql ржавый; вы можете попробовать

SELECT columns, count(table2.rev_id) As rev_count, 
    sum(table2.rev_rating) As sum_rev_rating,
    sum(table2.rev_rating)/count(table2.rev_id) as rev_ratio
FROM table1
    LEFT JOIN table2ON table1.dom_id = table2.rev_domain_from 
WHERE dom_lastreview != 0 
AND rev_status = 1 
GROUP BY dom_url 
ORDER BY rev_Ratio DESC

или

SELECT * from (
    SELECT columns, count(table2.rev_id) As rev_count, 
        sum(table2.rev_rating) As sum_rev_rating 
    FROM table1
        LEFT JOIN table2ON table1.dom_id = table2.rev_domain_from 
    WHERE dom_lastreview != 0 
    AND rev_status = 1 
    GROUP BY dom_url 
) X
ORDER BY X.sum_rev_rating/X.rev_count DESC

или

SELECT * from (
    SELECT columns, count(table2.rev_id) As rev_count, 
        sum(table2.rev_rating) As sum_rev_rating,
        sum(table2.rev_rating)/count(table2.rev_id) as rev_ratio
    FROM table1
        LEFT JOIN table2ON table1.dom_id = table2.rev_domain_from 
    WHERE dom_lastreview != 0 
    AND rev_status = 1 
    GROUP BY dom_url 
) X
ORDER BY rev_Ratio DESC