SQL novice here.
I have this schema:
What I need in plain English is:
"Out of the 2 columns, make one above the other in one column, and then count how many distincts values there is"
I've tried
SELECT COUNT (DISTINCT uid ) from nodes UNION SELECT COUNT (DISTINCT uid) from ways ;
SELECT distinct nodes.uid from nodes JOIN ways on nodes.uid = ways.uid ;
sqlite> SELECT COUNT (DISTINCT uid ) from nodes UNION SELECT COUNT (DISTINCT uid) from ways ;
1195
2182
sqlite> SELECT uid from nodes FULL OUTER JOIN ways on nodes.uid = ways.iud ;
Error: RIGHT and FULL OUTER JOINs are not currently supported
SELECT COUNT (DISTINCT iud) FROM (SELECT DISTINCT uid from nodes as uid UNION SELECT DISTINCT uid from ways as uid as subq);
SELECT count (distinct nodes.uid) from nodes JOIN ways on nodes.uid = ways.uid ;
takes ages and i'm not sure nodes.uid = ways.uid is the correct way to go
Any idea ?
I think i got it
SELECT COUNT (DISTINCT uid) from (SELECT DISTINCT uid from nodes UNION SELECT DISTINCT uid from ways) as subq ;
Since UNION returns a distinct set of the joining tables you dont need to use the DISTINCT keyword
SELECT COUNT(uid) Cnt
FROM (
SELECT uid
FROM nodes
UNION
SELECT uid
FROM ways
) t
Related
I want the count even if the count is 0. My current query is
SELECT `id`,count(0) as `fetchpc` FROM `user` WHERE pid in('4,6,7,8') GROUP BY `id`
But it returns only those id where count is greater than 0
Edit:
the values used for in('4,6,7,8') are first fetched from database in another query. And then using a script rows are converted to 4,6,7,8.
So all the values are present in the database.
Also it is possible that the values returned can go upto 100+ values.
You could left join this query on a "fictive" query that queries these IDs as literals:
SELECT ids.id, COALESCE(cnt, 0)
FROM (SELECT 4 AS id
UNION ALL
SELECT 6 AS id
UNION ALL
SELECT 7 AS id
UNION ALL
SELECT 8 AS id) ids
LEFT JOIN (SELECT id, COUNT(*) AS cnt
FROM fetchpc
GROUP BY id) t ON t.id = ids.id
You can use a derived table. I would recommend:
SELECT i.id, COUNT(u.id) as fetchpc
FROM (SELECT 4 as id UNION ALL
SELECT 6 as id UNION ALL
SELECT 7 as id UNION ALL
SELECT 8 as id
) i LEFT JOIN
`user` u
ON u.id = i.id
GROUP BY i.id;
From a performance perspective, this is much better than aggregating first (in a subquery) and then joining. Basically, the aggregation (in that case) has to aggregate all the data and afterwards filter out the unnecessary rows.
This formulation filters the rows first, which should speed the aggregation.
I have a query that gets some data about customers. This customers can have three phone numbers and these can be repeated.
To count the number of times that these phones are repeated a partner have create a subselect:
(select count(*)
from TABLE_A as k
where (k.phone=a.phone or k.phone2=a.phone or k.phone3=a.phone)
and k.id!=a.id) as repetitionsPhone1
This is inside a bigger select like this:
SELECT a.*,c.*,b.*,
(
select count(*)
from TABLE_A as k
where (k.phone=a.phone or k.phone2=a.phone or k.phone3=a.phone)
and k.id!=a.id
) as repetitionsPhone1
FROM a
left join c on a.id=c.id
left join b on a.id=b.id
This query takes for 50 rows about 30 seconds, and it should return about 2000 rows every single day.
To optimize this I use explain and I see that this subquery was the problem so I searched and I tried this:
SELECT phn,sum(count) as phoneRepetitions
from (
select k.phone1 as phn, count(*) as count
from k
group by k.phone1
UNION
select k.phone2 as phn,count(*) as count
from k
group by k.phone2
UNION
select k.phone3 as phn,count(*) as count
from k
group by k.phone3
) as aux
group by phn
And this returns #1062 MYSQL error: Duplicate entry for key 'distinct key'
First of all I would like to solve this problem. Anyone knows what is happening? This error seems logic in an insert statement, but in select?
And later, this will help to improve the big select that I must optimize? I will have to do this for the three columns.
Thank you.
SELECT count(*) from
(SELECT phones1 FROM k
union
SELECT phones2 from k
union
SELECT phones3 from k)
AS SumCountPhones
This seemed to work for me.
Solution as per How do I add two count(*) results together on two different tables?
You can keep stacking the unions.
SELECT
COUNT(*) AS CountOf FROM
table1
INNER JOIN
table2
GROUP BY phone1 , phone2 , phone3
HAVING COUNT(*) > 1
As sadly SQL is my weakest skill.
I'm trying to use UNION in a VIEW, where I can get statistics from two different tables with one query.
SELECT COUNT(*) AS `customer_count` FROM `Customers`
UNION
SELECT COUNT(*) AS `supplier_count` FROM `Suppliers`;
[Demo table]
However, it only returns customer_count, with two rows. Is there anyway, to make this work, so it returns customer_count and supplier_count separately?
You would need a cross join to see the results adjacent to each other in one row. So you would select from both the tables without a join condition.
select * from
(select count(*) as customer_count from Customers) x,
(select count(*) as supplier_count from Suppliers) y
select
(SELECT COUNT(*) FROM Customers) as customer_count,
(SELECT COUNT(*) FROM Suppliers) AS supplier_count
Using your Table Demo.
The key is use alias so the field names match on each union select.
In this case TableSource and Total
SELECT 'Customer' as TableSource, Count(City) as Total FROM Customers
UNION
SELECT 'Suppliers' as TableSource, Count(City) as Total FROM Suppliers;
CREATE VIEW `vw_count` AS
select (select count(0) from `tbl`) AS `customer_count`,
(select count(0) from `tbl2`) AS `supplier_count`;
I have the following query:
select distinct profile_id from userprofile_...
union
select distinct profile_id from productions_...
How would I get the count of the total number of results?
If you want a total count for all records, then you would do this:
SELECT COUNT(*)
FROM
(
select distinct profile_id
from userprofile_...
union all
select distinct profile_id
from productions_...
) x
you should use Union All if there are equals rows in both tables, because Union makes a distinct
select count(*) from
(select distinct profile_id from userprofile_...
union ALL
select distinct profile_id from productions_...) x
In this case, if you got a same Profile_Id in both tables (id is probably a number, so it's possible), then if you use Union, if you got Id = 1 in both tables, you will lose one row (it will appear one time instead of two)
This will perform pretty well:
select count(*) from (
select profile_id
from userprofile_...
union
select profile_id
from productions_...
) x
The use of union guarantees distinct values - union removes duplicates, union all preserves them. This means you don't need the distinct keyword (the other answers don't exploit this fact and end up doing more work).
Edited:
If you want to total number of different profile_id in each, where given values that appear in both table are considered different values, use this:
select sum(count) from (
select count(distinct profile_id) as count
from userprofile_...
union all
select count(distinct profile_id)
from productions_...
) x
This query will out-perform all other answers, because the database can efficiently count distinct values within a table much faster than from the unioned list. The sum() simply adds the two counts together.
These will not work if in one of the COUNT(*) the result is equals to 0.
This will be better:
SELECT SUM(total)
FROM
(
select COUNT(distinct profile_id) AS total
from userprofile_...
union all
select COUNT(distinct profile_id) AS total
from productions_...
) x
As omg ponies has already pointed out that there is no use of using distinct with UNION, you can use UNION ALL in your case.....
SELECT COUNT(*)
FROM
(
select distinct profile_id from userprofile_...
union all
select distinct profile_id from productions_...
) AS t1
Best solution is to add count of two query results. It will not be a problem if the table contains large number of records. And you don't need to use union query.
Ex:
SELECT (select COUNT(distinct profile_id) from userprofile_...) +
(select COUNT(distinct profile_id) from productions_...) AS total
I have this table:
Movies (ID, Genre)
A movie can have multiple genres, so an ID is not specific to a genre, it is a many to many relationship. I want a query to find the total number of movies which have at exactly 4 genres. The current query I have is
SELECT COUNT(*)
FROM Movies
GROUP BY ID
HAVING COUNT(Genre) = 4
However, this returns me a list of 4's instead of the total sum. How do I get the sum total sum instead of a list of count(*)?
One way would be to use a nested query:
SELECT count(*)
FROM (
SELECT COUNT(Genre) AS count
FROM movies
GROUP BY ID
HAVING (count = 4)
) AS x
The inner query gets all the movies that have exactly 4 genres, then outer query counts how many rows the inner query returned.
SELECT COUNT(*)
FROM (SELECT COUNT(*)
FROM movies
GROUP BY id
HAVING COUNT(genre) = 4) t
Maybe
SELECT count(*) FROM (
SELECT COUNT(*) FROM Movies GROUP BY ID HAVING count(Genre) = 4
) AS the_count_total
although that would not be the sum of all the movies, just how many have 4 genre's.
So maybe you want
SELECT sum(
SELECT COUNT(*) FROM Movies GROUP BY ID having Count(Genre) = 4
) as the_sum_total
What about:
SELECT COUNT(*) FROM (SELECT ID FROM Movies GROUP BY ID HAVING COUNT(Genre)=4) a