如何显示一个表在不同列中的mysql计数结果？

Question

I have got one table wit users. I want to collect girls and boys and display count numbers of them. I do this:

SELECT COUNT(`is_male`) AS 'boys' FROM `users` WHERE `is_male` = 1 UNION (SELECT COUNT(`is_male`) AS 'girls' FROM `users` WHERE `is_male` = 0) 

But it shows results in one column 'boys', how I can display one row with 2 columns 'boys' and 'girls'?

Answer 1

Just use conditional aggregation:

SELECT SUM(is_male = 1) AS boys,
       SUM(is_male = 0) as girls
FROM users ;

Notes:

• MySQL treats boolean expressions as numbers in a numeric context, with "1" as true and "0" as false (which is why this works).
• Only use single quotes for column and date constants, not for column names.
• There is no need to escape your column or table names. Queries with lots of back-ticks are harder to read.

Answer 2

You can use a conditional sum

SELECT SUM(is_male = 1) AS boys,
       SUM(is_male = 0) AS girls
FROM users

or count, but then the ELSE part has to be NULL since COUNT counts all non-null values

SELECT count(case when is_male = 1 then 1 else null end) AS boys,
       count(case when is_male = 0 then 1 else null end) AS girls
FROM users

Answer 3

That's conditional aggregation :

SELECT SUM(is_male) AS boys,
       SUM(is_male <> 1) AS girls
FROM users;

MySQL evaluates Boolean expressions as 1 and 0 , so no need for case expression or anything .