Mysql 为不同的 where 子句显示不同的列

Question

I want to show a output table that counts all the users found in a table. Basically I want the output to look like:

+-----------+-----------+
| user1     | user2     |
+-----------+-----------+
|         5 |         2 |
+-----------+-----------+

I'm just using a dummy table to test this. My query looks like this:

(
    select 
        name as user1 
    from 
        users 
    where 
        name = 'root'
) UNION (
    select 
        name as user2 
    from
        users 
    where 
        name = 'not_root'
)

Which only outputs something like this:

+-----------+
| user1     |
+-----------+
|         5 |
|         2 |
+-----------+

Answer 1

EDITED

The main idea of the approach it's treat a table as two different virtual tables in subquery. We can make nested select statement eg (select count(*) as c from users where name = 'root') u1 MySql treats it as particular table named u1 with one row and one column named c .

select u1.c as root_cnt, u2.c as not_root_cnt
from (select count(*) as c from users where name = 'root') u1,
(select count(*) as c from users where name = 'not_root') u2

or

Moreover if you have select statement that returns only one row you can put nested selects directly in fields list

select (select count(*) as c from users where name = 'root') as root_cnt, (select count(*) as c from users where name = 'not_root') as not_root_cnt

Definite disadvantage of such approach it's extra subqueries. Method based on using case when construction free from such disadvantage.

Answer 2

Try this

SELECT
    SUM(CASE WHEN Name = 'root' THEN 1 ELSE 0 END) user1,
    SUM(CASE WHEN Name = 'not_root' THEN 1 ELSE 0 END) user2
FROM Users

Answer 3

You can use a case statement inside of count to get the counts in separate columns

select
    count(case when name = 'root' then 1 end) user1,
    count(case when name = 'not_root' then 1 end) user2
from users
where name in ('root','not_root')

Answer 4

It seems your query is wrong..

union won't combine the results of two queries in the way you have described above.

union would combine the result of two or more select statements but wouldn't "join" it.

You might want to use joins for this cause. still you wouldn't be able to put 5|2 in same row as it basically suggests --> fetch user 1 and user 2 values for one particular type

Answer 5

i think group by is a much better approach: select user, count(user) from users group by user