Question

鉴于以下查询，如何返回具有最多事务的p_name？类似地，如何返回具有最多事务的t_amount。我当然希望在这一个查询中完成所有操作。

SELECT t.*, p.* 
FROM transactions t
LEFT JOIN partners p ON p.id=t.partner_id

可以返回类似的内容：

t_amount     t_platform      t_user     p_id      p_name

100.00       windows         122         20       simmons
200.00       windows         211         20       simmons
100.00       mac             200         18       smith
100.00       linux           190         20       simmons
100.00       mac             100         18       smith

所以给定结果集，我会回来best_partner = simmons和best_amount = 100.00

谢谢！

Answer 1

我认为“最佳合作伙伴”=交易数量最多的合伙人和“最佳金额”=最常发生的交易金额。

要计算事务，可以使用Count（）函数和group by。像这样：

SELECT p.name,count(t.id) as transactionCount
FROM transactions t
LEFT JOIN partners p ON p.id=t.partner_id
GROUP BY p.name
ORDER BY 2 DESC 
LIMIT 1

类似于“最佳金额”：

SELECT t.amount, Count(t.id) as transactionAmountCount
FROM transactions t
LEFT JOIN partners p ON p.id=t.partner_id
GROUP BY t.amount
ORDER BY 2 DESC 
LIMIT 1

编辑：合并为两个子查询：

SELECT
(SELECT p.name
FROM transactions t
LEFT JOIN partners p ON p.id=t.partner_id
GROUP BY p.name
ORDER BY count(t.id) DESC 
LIMIT 1) as best_partner
,
(SELECT t.amount
FROM transactions t
LEFT JOIN partners p ON p.id=t.partner_id
GROUP BY t.amount
ORDER BY Count(t.id) DESC 
LIMIT 1) as most_occuring_transaction_amount

Answer 2

SELECT p.*, COUNT(p.id) AS p_count
FROM transactions t
LEFT JOIN partners p ON p.id=t.partner_id
GROUP BY p_count
ORDER BY p_count DESC
LIMIT 1

计算字段值的大多数出现次数

2 个答案: