I have a table say tbl_test. In this table I have 2.4 million records. I run the following three queries which are very very slow and frustrating.
select count(*) from tbl_test;
-- 2.4 mil records in ~9 seconds
select count(*) from tbl_test where status = 'active';
-- 2.4 mil records in ~9 seconds
select count(*) from tbl_test where status = 'inactive';
-- 0 records in ~0 seconds
I have created a view say view_tbl_test using the following query:
create view view_tbl_test as
select * from
(select count(*) count_active from tbl_test where status = 'active' ) x,
(select count(*) count_inactive from tbl_test where status = 'inactive' ) y,
(select count(*) count_total from tbl_test) z
Now, I am picking only the single row from the view and its taking the same amount of time like previous.
select * from view_tbl_test limit 1;
Am I doing something wrong here? Is there any way which can make the view to return data in ~0 seconds?
Your statement runs three selects on the table. This can be done with a single statement:
create view view_tbl_test
as
select count(case when status = 'active' then 1 end) as count_active
count(case when status = 'inactive' then 1 end) as count_inactive,
count(*) as count_total
from tbl_test;
This should run in approx. 9seconds as it essentially does the same as your first statement.
The last statement is probably that fast because you have an index on status but as you did not provide the execution plans, this is nearly impossible to tell.
Related
I have a problem with my SQL command. I want to select 2 movies which 2 movies sum of durations less than 150 I wrote this SQL command:
Select
movie_title,Sum(movie_time) as sum_movie
From
movie_movie
Group By
movie_title
Having
Sum(movie_time)<100
Order By
sum_movie DESC
You can get two movies with minimum movie_time values with order by movie_time ASC limit 2 in CTE, and then use that in the condition.
with two_min_movie as (
select *
from movie_movie
order by movie_time ASC limit 2
)
select *
from two_min_movie
where (select sum(movie_time) from two_min_movie) < 150
Demo in DBfiddle
I have created the following query:
select t.id, t.row_id, t.content, t.location, t.retweet_count, t.favorite_count, t.happened_at,
a.id, a.screen_name, a.name, a.description, a.followers_count, a.friends_count, a.statuses_count,
c.id, c.code, c.name,
t.parent_id
from tweets t
join accounts a on a.id = t.author_id
left outer join countries c on c.id = t.country_id
where t.row_id > %s
-- order by t.row_id
limit 100
Where %s is a number that starts at 0 and is incremented by 100 after each such query is conducted. I want to fetch all records from the database using this method, where I just increase the %s in the where condition. I found this approach on https://ivopereira.net/efficient-pagination-dont-use-offset-limit. I also included a column in my table which is corresponding to row number (I named it row_id). Now the problem is when I run this query the first time, it returns rows which have an row_id of 3 million. I would like the cursor (not sure if my terminology is correct) to start from rows with row_id 1 through 100 and so on. The table contains 7 million rows. Am I missing something obvious with which I could achieve my goal?
Query in English:
Retrieve a random row from stuff.
row is not mentioned in done.
row belongs to the highest* scored friend.
*if no rows that belong to highest scored friend are found, take the next friend, an so on.
My current query takes too long to complete, because it is randomly ordering all stuff, while it should randomly order batch after batch.
Here is an sqlfiddle with tables and data.
My query:
WITH ordered_friends AS (SELECT *
FROM friends
ORDER BY score DESC)
SELECT s.stuff_id
FROM ordered_friends
INNER JOIN (SELECT *
FROM stuff
ORDER BY random()) AS s ON s.owner = ordered_friends.friend
WHERE NOT EXISTS(
SELECT 1
FROM done
WHERE done.me = 42
AND done.friend = s.owner
AND done.stuff_id = s.stuff_id
)
-- but it should keep the order of ordered_friends (score)
-- it does not have to reorder all stuff
-- one batch for each friend is enough until a satisfying row is found.
LIMIT 1;
How about this?
SELECT s.stuff_id
FROM friends
CROSS JOIN LATERAL (SELECT stuff_id
FROM stuff
WHERE stuff.owner = friends.friend
AND NOT EXISTS(SELECT 1
FROM done
WHERE done.me = 42
AND done.friend = stuff.owner
AND done.stuff_id = stuff.stuff_id
)
ORDER BY random()
LIMIT 1
) s
ORDER BY friends.score DESC
LIMIT 1;
The following indexes would make it fast:
CREATE INDEX ON friends(score); -- for sorting
CREATE INDEX ON stuff(owner); -- for the nested loop
CREATE INDEX ON done(stuff_id, friend); -- for NOT EXISTS
The code is roughly like this:
WITH cte AS
(
SELECT TOP 4 id, due_date, check
FROM table_a a
INNER JOIN table_b b ON a.linkid = b.linkid
WHERE
b.status = 1
AND due_date > GetDate()
ORDER BY due_date, id
)
UPDATE cte
SET check = 1
OUTPUT
INSERTED.id,
INSERTED.due_date
Note: the actual data has same due_date.
When I ran the SELECT statement only inside the cte, I could get the result, for ex: 1, 2, 3, 4.
But after the UPDATE statement, the updated results are: 4, 1, 2, 3
Why is this (order-change) happening?
How to keep or re-order the results back to 1,2,3,4 in this same 1 query?
In MSDN https://msdn.microsoft.com/pl-pl/library/ms177564(v=sql.110).aspx you can read that
There is no guarantee that the order in which the changes are applied
to the table and the order in which the rows are inserted into the
output table or table variable will correspond.
Thats mean you can't solve your problem with only one query. But you still can use one batch to do what you need. Because your output don't guarantee the order then you have to save it in another table and order it after update. This code will return your output values in order that you assume:
declare #outputTable table( id int, due_date date);
with cte as (
select top 4 id, due_date, check
from table_a a
inner join table_b b on a.linkid = b.linkid
where b.status = 1
and due_date > GetDate()
order by due_date, id
)
update cte
set check = 1
output inserted.id, inserted.due_date
into #outputTable;
select *
from #outputTable
order by due_date, id;
I have the following table
-----Account#----Period-----Balance
12345---------200901-----$11554
12345---------200902-----$4353
12345 --------201004-----$34
12345 --------201005-----$44
12345---------201006-----$1454
45677---------200901-----$14454
45677---------200902-----$1478
45677 --------201004-----$116776
45677 --------201005-----$996
56789---------201006-----$1567
56789---------200901-----$7894
56789---------200902-----$123
56789 --------201003-----$543345
56789 --------201005-----$114
56789---------201006-----$54
I want to select the account# that have a period of 201005.
This is fairly easy using the code below. The problem is that if a user enters 201003-which doesnt exist- I want the query to select the previous value.*NOTE that there is an account# that has a 201003 period and I still want to select it too.*
I tried CASE, IF ELSE, IN but I was unsuccessfull.
PS:I cannot create temp tables due to system limitations of 5000 rows.
Thank you.
DECLARE #INPUTPERIOD INT
#INPUTPERIOD ='201005'
SELECT ACCOUNT#, PERIOD , BALANCE
FROM TABLE1
WHERE PERIOD =#INPUTPERIOD
SELECT t.ACCOUNT#, t.PERIOD, t.BALANCE
FROM (SELECT ACCOUNT#, MAX(PERIOD) AS MaxPeriod
FROM TABLE1
WHERE PERIOD <= #INPUTPERIOD
GROUP BY ACCOUNT#) q
INNER JOIN TABLE1 t
ON q.ACCOUNT# = t.ACCOUNT#
AND q.MaxPeriod = t.PERIOD
select top 1 account#, period, balance
from table1
where period >= #inputperiod
; WITH Base AS
(
SELECT *, ROW_NUMBER() OVER (ORDER BY Period DESC) RN FROM #MyTable WHERE Period <= 201003
)
SELECT * FROM Base WHERE RN = 1
Using CTE and ROW_NUMBER() (we take all the rows with Period <= the selected date and we take the top one (the one with auto-generated ROW_NUMBER() = 1)
; WITH Base AS
(
SELECT *, 1 AS RN FROM #MyTable WHERE Period = 201003
)
, Alternative AS
(
SELECT *, ROW_NUMBER() OVER (ORDER BY Period DESC) RN FROM #MyTable WHERE NOT EXISTS(SELECT 1 FROM Base) AND Period < 201003
)
, Final AS
(
SELECT * FROM Base
UNION ALL
SELECT * FROM Alternative WHERE RN = 1
)
SELECT * FROM Final
This one is a lot more complex but does nearly the same thing. It is more "imperative like". It first tries to find a row with the exact Period, and if it doesn't exists does the same thing as before. At the end it unite the two result sets (one of the two is always empty). I would always use the first one, unless profiling showed me the SQL wasn't able to comprehend what I'm trying to do. Then I would try the second one.