为什么我的涉及除法和COUNT的查询总是结果为1？

您正在尝试计算不重复的行，但不使用

count(distinct ...)

SELECt     COUNT(distinct c.id) as "Total Customers",    COUNT(distinct p.id) as "Total Sales",    COUNT(distinct c.id) * 1.00 / COUNT(distinct p.id) as "Sales per customer"FROM test_customers c    LEFT OUTER JOIN test_purchases p ON c.id = p.cid

注意，性能不是很好