计算唯一值的数量 [英] Count number of unique values

问题描述

如果我有三列:

orderNumber, name, email

我想计算一下表格中有多少唯一的电子邮件，我该怎么做呢?

and I would like to count how many unique emails are in the table how would I go about doing so?

这样的声明:

SELECT count(email) FROM orders

给我总数.

我尝试了SELECT DISTINCT count(email) FROM orders

但这似乎并没有给我我期望的数字.

but that does not seem to be giving me the numbers I am expecting.

推荐答案

使用

SELECT count( DISTINCT(email) ) FROM orders

不同提供唯一的电子邮件ID，然后简单地对它们进行计数.

Distinct provide unique email ids and then simply count them.

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