I have two tables, question & field. I need to count entries , with coincidental value of template_id (both tables contains).
Please advice, how to do it?
select count(q.*)
from question q
left join field f on f.template.id = q.template_id
In StackOverflow one should show ones own attempt, show that some effort was done.
Above inner join is probably what you meant. Try first select q.*, f.*.
SELECT
COUNT(*) AS TotalRecords
FROM question q
INNER JOIN field f ON f.template_id = q.template_id
If you want the count of distinct template_id in the two tables, use JOIN and COUNT(DISTINCT):
select count(distinct q.template_id)
from question q join
field f
on f.template_id = q.template_id;
If you use count(*) you will get a count of matching rows, not template_ids, so duplicates will affect the result.
If template_id is known to be unique in one of the tables (say question), then exists is probably more efficient:
select count(*)
from question q
where exists (select 1
from field f
where f.template_id = q.template_id
);
Related
All i want to do is to join two tables, list ALL the rows from the first table, find the average from the second table from all the rows, then list only the ones that are greater than the average.
This is wahat i have done so far, and i am only getting one greater than the average but there are others.
SELECT winner_age, AVG(actor_age) FROM oscar_winners
INNER JOIN actors ON actors.id = oscar_winners.id
WHERE winner_age > (
SELECT AVG(actor_age)
)
You don't really need a join here:
SELECT o.WINNER_AGE
FROM OSCAR_WINNERS o
WHERE o.WINNER_AGE > (SELECT AVG(a.ACTOR_AGE)
FROM ACTORS a)
Something like this?
SELECT actors.*, (SELECT AVG(actor_age) from actors) as average
FROM oscar_winners
INNER JOIN actors ON actors.id = oscar_winners.id and actors.winner_age > (SELECT AVG(actor_age) from actors)
The problem with your query is because you are using a where clause, while you should probably be using having:
SELECT w.winner_age, AVG(a.actor_age)
FROM oscar_winners w
INNER JOIN actors a
ON actors.id = oscar_winners.id
group by w.winner_age
having w.winner_age > AVG(a.actor_age)
i have following sql in java project:
select distinct * from drivers inner join licenses on drivers.user_id=licenses.issuer_id
inner join users on drivers.user_id=users.id
where (licenses.state='ISSUED' or drivers.status='WAITING')
and users.is_deleted=false
And result i database looks like this:
And i would like to get only one result instead of two duplicated results.
How can i do that?
Solution 1 - That's Because one of data has duplicate value write distinct keyword with only column you want like this
Select distinct id, distinct creation_date, distinct modification_date from
YourTable
Solution 2 - apply distinct only on ID and once you get id you can get all data using in query
select * from yourtable where id in (select distinct id from drivers inner join
licenses
on drivers.user_id=licenses.issuer_id
inner join users on drivers.user_id=users.id
where (licenses.state='ISSUED' or drivers.status='WAITING')
and users.is_deleted=false )
Enum fields name on select, using COALESCE for fields which value is null.
usually you dont query distinct with * (all columns), because it means if one column has the same value but the rest isn't, it will be treated as a different rows. so you have to distinct only the column you want to, then get the data
I suspect that you want left joins like this:
select *
from users u left join
drivers d
on d.user_id = u.id and d.status = 'WAITING' left join
licenses l
on d.user_id = l.issuer_id and l.state = 'ISSUED'
where u.is_deleted = false and
(d.user_id is not null or l.issuer_id is not null);
I have two tables that are structured the same with a sequence column and I am trying to count the number of sequences that show up in two different tables.
I am using this right now:
SELECT A.sequence FROM p2.pool A WHERE EXISTS (SELECT * from
p1.pool B WHERE B.sequence = A.sequence)
And then I was going to count the number of results.
Is there an easier way to do this using COUNT so I don't have to get all of the results first?
Yes, there is an easier way using COUNT:
SELECT COUNT(*)
FROM p2.pool A
WHERE EXISTS (SELECT *
FROM p1.pool B
WHERE B.sequence = A.sequence)
You could also use a join instead of a subquery, but the speed is unlikely to change:
SELECT COUNT(*)
FROM p2.pool A
JOIN p1.pool B ON A.sequence = B.sequence
I have two tables
Table A
type_uid, allowed_type_uid
9,1
9,2
9,4
1,1
1,2
24,1
25,3
Table B
type_uid
1
2
From table A I need to return
9
1
Using a WHERE IN clause I can return
9
1
24
SELECT
TableA.type_uid
FROM
TableA
INNER JOIN
TableB
ON TableA.allowed_type_uid = TableB.type_uid
GROUP BY
TableA.type_uid
HAVING
COUNT(distinct TableB.type_uid) = (SELECT COUNT(distinct type_uid) FROM TableB)
Join the two tables togeter, so that you only have the records matching the types you are interested in.
Group the result set by TableA.type_uid.
Check that each group has the same number of allowed_type_uid values as exist in TableB.type_uid.
distinct is required only if there can be duplicate records in either table. If both tables are know to only have unique values, the distinct can be removed.
It should also be noted that as TableA grows in size, this type of query will quickly degrade in performance. This is because indexes are not actually much help here.
It can still be a useful structure, but not one where I'd recommend running the queries in real-time. Rather use it to create another persisted/cached result set, and use this only to refresh those results as/when needed.
Or a slightly cheaper version (resource wise):
SELECT
Data.type_uid
FROM
A AS Data
CROSS JOIN
B
LEFT JOIN
A
ON Data.type_uid = A.type_uid AND B.type_uid = A.allowed_type_uid
GROUP BY
Data.type_uid
HAVING
MIN(ISNULL(A.allowed_type_uid,-999)) != -999
Your explanation is not very clear. I think you want to get those type_uid's from table A where for all records in table B there is a matching A.Allowed_type_uid.
SELECT T2.type_uid
FROM (SELECT COUNT(*) as AllAllowedTypes FROM #B) as T1,
(SELECT #A.type_uid, COUNT(*) as AllowedTypes
FROM #A
INNER JOIN #B ON
#A.allowed_type_uid = #B.type_uid
GROUP BY #A.type_uid
) as T2
WHERE T1.AllAllowedTypes = T2.AllowedTypes
(Dems, you were faster than me :) )
Is it allowed to reference external field from nested select?
E.g.
SELECT
FROM ext1
LEFT JOIN (SELECT * FROM int2 WHERE int2.id = ext1.some_id ) as x ON 1=1
in this case, this is referencing ext1.some_id in nested select.
I am getting errors in this case that field ext1.some_id is unknow.
Is it possible? Is there some other way?
UPDATE:
Unfortunately, I have to use nested select, since I am going to add more conditions to it, such as LIMIT 0,1
and then I need to use a second join on the same table with LIMIT 1,1 (to join another row)
The ultimate goal is to join 2 rows from the same table as if these were two tables
So I am kind of going to "spread" a few related rows into one long row.
The answer to your initial question is: No, remove your sub-query and put the condition into the ON-clause:
SELECT *
FROM ext1
LEFT JOIN int2 ON ( int2.id = ext1.some_id )
One solution could be to use variables to find the first (or second) row, but this solution would not work efficiently with indexes, so you might end up with performance problems.
SELECT ext1.some_id, int2x.order_col, int2x.something_else
FROM ext1
LEFT JOIN (SELECT `int2`.*, #i:=IF(#id=(#id:=id), #i+1, 0) As rank
FROM `int2`,
( SELECT #i:=0, #id:=-1 ) v
ORDER BY id, order_col ) AS int2x ON ( int2x.id = ext1.some_id
AND int2x.rank = 0 )
;
This assumes that you have a column that you want to order by (order_col) and Left Joins the first row per some_id.
Do you mean this?
SELECT ...
FROM ext1
LEFT JOIN int2 ON int2.id=ext1.some_id
That's what the ON clause is for:
SELECT
FROM ext1
LEFT JOIN int2 AS x ON x.id = ext1.some_id