SQL获取每个值的不同行的计数

Question

I don't have much experience to SQL, and I can't seem to figure out this problem.

If I have a table like this:

Installs

id   user
1    bob
2    carl
2    carl
2    charles
3    bill
3    bill

and another like this:

Apps

id   name
1    app1
2    app2
3    app3

How would I get something like this?:

name   distinct_users
app1   1
app2   2
app3   1

I have tried this:

select apps.name, count(distinct installs.user) 
from installs, apps 
where installs.id = apps.id;

but that only yields one row because it is counting the total number of distinct users in installs.

app1 4

Answer 1

You are missing a group by clause to get result per app :

SELECT   apps.name, COUNT(distinct installs.user) 
FROM     installs, apps 
WHERE    installs.id = apps.id;
GROUP BY apps.name

Note, by the way, the implicit joins (having more than one table in the from clause have been considered to be deprecated for quite a while now. Instead, it's recommended you use an explicit join:

SELECT   apps.name, COUNT(distinct installs.user) 
FROM     installs
JOIN     apps ON installs.id = apps.id;
GROUP BY apps.name

Answer 2

Use group by and count(*)

Select apps.name, count(*) 
from installs 
inner join  apps  on  installs.id = apps.id
group by apps.name;

Answer 3

You need to add the GROUP BY .
More over avoid comma separated table concepts and use JOIN with ON.
Add alias name for each table to the better readability.

SELECT A.name, COUNT(DISTINCT I.user) 
FROM apps A
INNER JOIN installs I ON I.id = A.id
GROUP BY A.name;

Answer 4

SELECT `apps`.`name`, COUNT(DISTINCT(`installs`.`user`)) 
FROM `installs`, `apps` 
WHERE `installs`.`id` = `apps`.`id`
GROUP BY `apps`.`id`;

See this fiddle .