I'm currently using the following query (simplified indeed) :
SELECT
(
SELECT COUNT(id)
FROM bla_1
WHERE id NOT IN (SELECT id FROM blahhh)
)
+
(
SELECT COUNT(id)
FROM bla_2
WHERE id NOT IN (SELECT id FROM blahhh)
)
as count
Before somebody mentions it, may i add bla_1 and bla_2 don't contain the same data, even if with that simplified query it might seem so.
The problem here is that some ids counted by the second query are already taken care of by the first one. In other words, the second query could return '2', and one of those 2 counted rows would already be counted by the first query.
So, since both queries have some ids in common that i don't want to count twice, i came up with that :
SELECT
(
SELECT COUNT(id)
FROM bla_1
WHERE id NOT IN (SELECT id FROM blahhh)
)
+
(
SELECT COUNT(id)
FROM bla_2
WHERE id NOT IN (SELECT id FROM blahhh)
AND id NOT IN (SELECT id
FROM bla_1
WHERE id NOT IN (SELECT id FROM blahhh)
)
)
as count
You will notice that the second subquery inside the second query is the exact same query as the first one.
My problem is that i can't get to make this work without executing the same query twice (a first time to count results, and a second time to actually retrieve those results).
Much love to the one solving that problem :-)
Try using the UNION operation that will eliminate duplicates for you.
SELECT COUNT(ID) AS MyCount
FROM
( SELECT ID FROM Table1 WHERE /*....*/
UNION
SELECT ID FROM Table2 WHERE /*....*/
) r
Related
The following query:
SELECT * FROM table WHERE id IN (1,2,3);
will return three records.
SELECT * FROM table WHERE id IN (1,2,1);
will return just two records (for Ids 1 and 2)
Is there a way for the result set to contain two records for Id 1 (and three in total)?
You could try creating a table for the ids you want to filter by. This would get you your desired results. I'm not sure if mysql supports CTE, but hopefully this is enough for you to get the idea.
WITH IDS
AS
(
SELECT 1 AS id
UNION ALL
SELECT 2 AS id
UNION ALL
SELECT 1 AS id
)
SELECT T.*
FROM T
JOIN IDS
ON T.id = IDS.id
I can't seem to find a good way to select unique data. Specifically unique values within a query.
Here's an example:
A select distinct query returns 10,000 rows. Within those rows, one column - let's call it vendors - has maybe 6 unique values. How can I return just the 6 unique vendors without scrolling through 10,000 records to make sure I caught them all. Even sorting by vendor this would still be a daunting task.
select distinct vendor from (select [distinct] col1, col2, ..., vendor from your_table) temp;
On the other hand you could ask directly for the distinct vendor, without running the more expensive query:
select distinct vendor from yourtable where {your_criteria}
Maybe you shoud try to give alias to your query result that returns 10k rows
something like (SELECT DISTINCT FROM ... ) as yourtable
and then do SELECT DISTINCT your column name FROM yourtable
(SELECT DISTINCT * FROM xxx ) as yourtable // this would return your 10k rows and nam that table simply yourtable
and then SELECT DISTINCT youruniquecolumn FROM yourtable // this will select all unique columns from your 10k table
I have a MySQL table where I have a certain id as a foreign key coming from another table. This id is not unique to this table so I can have many records holding the same id.
I need to find out which ids are seen the least amount of times in this table and pull up a list containing them.
For example, if I have 5 records with id=1, 3 records with id=2 and 3 records with id=3, I want to pull up only ids 2 & 3. However, the data in the table changes quite often so I don't know what that minimum value is going to be at any given moment. The task is quite trivial if I use two queries but I'm trying to do it with just one. Here's what I have:
SELECT id
FROM table
GROUP BY id
HAVING COUNT(*) = MIN(SELECT COUNT(*) FROM table GROUP BY id)
If I substitute COUNT(*) = 3, then the results come up but using the query above gives me an error that MIN is not used properly. Any tips?
I would try with:
SELECT id
FROM table
GROUP BY id
HAVING COUNT(*) = (SELECT COUNT(*) FROM table GROUP BY id ORDER BY COUNT(*) LIMIT 1);
This gets the minimum selecting the first row from the set of counts in ascendent order.
You need a double select in the having clause:
SELECT id
FROM table
GROUP BY id
HAVING COUNT(*) = (SELECT MIN(cnt) FROM (SELECT COUNT(*) as cnt FROM table GROUP BY id) t);
The MIN() aggregate function is suposed to take a column, not a query. So, I see two ways to solve this:
To properly write the subquery, or
To use temp variables
First alternative:
select id
from yourTable
group by id
having count(id) = (
select min(c) from (
select count(*) as c from yourTable group by id
) as a
)
Second alternative:
set #minCount = (
select min(c) from (
select count(*) as c from yourTable group by id
) as a
);
select id
from yourTable
group by id
having count(*) = #minCount;
You need to GROUP BY to produce a set of grouped values and additional select to get the MIN value from that group, only then you can match it against having
SELECT * FROM table GROUP BY id
HAVING COUNT(*) =
(SELECT MIN(X.CNT) AS M FROM(SELECT COUNT(*) CNT FROM table GROUP BY id) AS X)
I have the following table:
CREATE TABLE sometable (my_id INTEGER PRIMARY KEY AUTOINCREMENT, name STRING, number STRING);
Running this query:
SELECT * FROM sometable;
Produces the following output:
1|someone|111
2|someone|222
3|monster|333
Along with these three fields I would also like to include a count representing the amount of times the same name exists in the table.
I've obviously tried:
SELECT my_id, name, count(name) FROM sometable GROUP BY name;
though that will not give me an individual result row for every record.
Ideally I would have the following output:
1|someone|111|2
2|someone|222|2
3|monster|333|1
Where the 4th column represents the amount of time this number exists.
Thanks for any help.
You can do this with a correlated subquery in the select clause:
Select st.*,
(SELECT count(*) from sometable st2 where st.name = st2.name) as NameCount
from sometable st;
You can also write this as a join to an aggregated subquery:
select st.*, stn.NameCount
from sometable st join
(select name, count(*) as NameCount
from sometable
group by name
) stn
on st.name = stn.name;
EDIT:
As for performance, the best way to find out is to try both and time them. The correlated subquery will work best when there is an index on sometable(name). Although aggregation is reputed to be slow in MySQL, sometimes this type of query gets surprisingly good results. The best answer is to test.
Select *, (SELECT count(my_id) from sometable) as total from sometable
I have collected informations from different sources about certain IDs that should match a single name. Some sources are more trustworthy than others in giving the correct name for a given ID.
I created a table (name, id, source_trustworthiness) and I want to get the most trustworthy name for each ID.
I tried
SELECT name, id, MAX( source_trustworthiness )
FROM table
GROUP BY id
this returns th highest trustworthiness available for each ID but with the first name it finds, regarless of its trustworthiness.
Is there a way I can get that right ?
Mysql has special functionality to help:
SELECT * FROM (
SELECT name, id, source_trustworthiness
FROM table
ORDER BY 3 DESC ) x
GROUP BY id
Although this wouldn't even execute in other databases (not naming all non-aggregate columns in the GROUP BY clause), with mysql it returns the first row encountered for each unique value of the grouped by columns. By ordering the rows greatest first, the first row for each id will be the most trustworthy.
Since this question is tagged mysql, this query is OK. Not only is it really simple, it's also quite fast.
SELECT a.*
FROM TableName a
INNER JOIN
(
SELECT id, MAX(source_trustworthiness) max_val
FROM TableName
GROUP BY ID
) b ON a.ID = b.ID AND
a.source_trustworthiness = b.max_val