I'm building an ionic 2 App, where I store some local data via sqlite. I have 2 seperate tables called history and favorites.
my history table has the columns called
id,answer,time
and my favorites table
id, likevalue, time.
I now want to query the last x rows of history and append the column likevalue by the same id from favorites by the latest likevalue of the same id, if there is no likevalue for the same id, it should be set as none or null.
If this is to complicated to understand, i will take the time to illustrate the problem by tables.
thanks in advance
solved it with a subquery
SELECT h.*,
(SELECT likevalue FROM favorites AS f WHERE h.id = f.id ORDER BY f.time DESC LIMIT 1 ) AS like
FROM history AS h
ORDER BY h.time DESC
LIMIT ?,?
Related
I have a table like this:
Assume there are lots of Names (i.e., E,F,G,H,I etc.,) and their respective Date and Produced Items in this table. It's a massive table, so I'd want to write an optimised query.
In this, I want to query the latest A,B,C,D records.
I was using the following query:
SELECT * FROM c WHERE c.Name IN ('A','B','C','D') ORDER BY c.Date DESC OFFSET 0 LIMIT 4
But the problem with this query is, since I'm ordering by Date, the latest 4 records I'm getting are:
I want to get this result:
Please help me in modifying the query. Thanks.
I have a table holding information about contacts made to many different customers in the format
email_address | treatment_group | customer_id | contact_date |
I am trying to add a column that looks at each distinct customer and numbers the contacts they've received from longest ago to most recent. I'm using this code:
explain create table db.responses_with_rank
as
( select a.*,
rank () over (partition by customer_id order by contact_date asc)as xrank
from db.responses_with_rank
)
with data
primary index (email_address, treatment_group)
My query is spooling out. There is a primary index of email_address, treatment_group that leads to a skew factor of 1.1 and a secondary primary index on customer_id. I've collected statistics on both sets of indexes. The table is quite large - around 200M records. Is there something I can try to optimize this query?
There is not enough information to determine the cause of the error.
For start, please add the following to your question:
TD version (select * from dbc.dbcinfo)
Execution plan
The statistics collection commands you have used
customer_id top frequencies (select top 10 customer_id,count(*) from db.responses_with_rank group by 1 order by 2 desc)
Do you have wide text columns in your table?
P.s.
I strongly recommend to use create multiset table and not create table.
I'm new to SQL(ite), so i'm sorry if there is a simple answer i just were to stupid to find the right search terms for.
I got 2 tables: 1 for user information and another holding points a user achieved. It's a simple one to many relation (a user can achieve points multiple times).
table1 contains "userID" and "Username" ...
table2 contains "userID" and "Amount" ...
Now i wanted to get a highscore rank for a given username.
To get the highscore i did:
SELECT Username, SUM(Amount) AS total FROM table2 JOIN table1 USING (userID) GROUP BY Username ORDER BY total DESC
How could i select a single Username and get its position from the grouped and ordered result? I have no idea how a subselect would've to look like for my goal. Is it even possible in a single query?
You cannot calculate the position of the user without referencing the other data. SQLite does not have a ranking function which would be ideal for your user case, nor does it have a row number feature that would serve as an acceptable substitute.
I suppose the closest you could get would be to drop this data into a temp table that has an incrementing ID, but I think you'd get very messy there.
It's best to handle this within the application. Get all the users and calculate rank. Cache individual user results as necessary.
Without knowing anything more about the operating context of the app/DB it's hard to provide a more specific recommendation.
For a specific user, this query gets the total amount:
SELECT SUM(Amount)
FROM Table2
WHERE userID = ?
You have to count how many other users have a higher amount than that single user:
SELECT COUNT(*)
FROM table1
WHERE (SELECT SUM(Amount)
FROM Table2
WHERE userID = table1.userID)
>=
(SELECT SUM(Amount)
FROM Table2
WHERE userID = ?);
I have a relatively simple select query which asks for rows by an column value (this is not controlled by me). I pass in a variable argument of id values to be returned. Here's an example:
select * from team where id in (2, 1, 3)
I'm noticing that as the database changes its order over time, my results are changing order as well. Is there a way to make SQLite guarantee results in the same order as the arguments?
If you could have so many IDs that the query becomes unwieldy, use a temporary table to store them:
CREATE TEMPORARY TABLE SearchIDs (
ID,
OrderNr INTEGER PRIMARY KEY
);
(The OrderNr column is autoincrementing so that it automatically gets proper values when you insert values.)
To do the search, you have to fill this table:
INSERT INTO SearchIDs(ID) VALUES (2), (1), (3) ... ;
SELECT Team.*
FROM Team
JOIN SearchIDs USING (ID)
ORDER BY SearchIDs.OrderNr;
DELETE FROM SearchIDs;
Try this!
select * from team order by
case when 2 then 0
when 1 then 1
when 3 then 2
end
I have database with with roughly following structure:
table1 (name) -< table2 -< table3 (score)
where -< means 1 to many relationship. What i need to do is for every string in a given list find the linked entry from table3 with a maximum score value. The way i do it now is quite slow, and i wonder of it could be sped up.
How i am doing this:
SELECT k.score,k.yaw,k.pitch,k.roll,k.kp_number,k.ke_number,k.points,k.elems --various fields of third table
FROM File
JOIN FaceDetection AS d ON d.f_id=File.file_id --joining second table
JOIN FaceKey AS k ON k.face_det=d.fd_id --joining third table
WHERE name=:fld
ORDER BY k.score DESC
I open transaction, prepare query with the above text, and in cycle retrieve the entries i am interested in from the database, then commit transaction. What are better, faster ways?
Indexes can be used for all the columns that are used for lookups or sorting, but a query cannot use more than one index per table.
Check the EXPLAIN QUERY PLAN output to see whether this query does table scans or uses indexes.
You are not returning values from any table but FaceKey, so you do not actually need to do a join.
However, rewriting the query as below might or might not help:
SELECT score,
yaw,
pitch,
roll,
kp_number,
ke_number,
points,
elems
FROM FaceKey
WHERE face_det IN (SELECT fd_id
FROM FaceDetection
WHERE f_id IN (SELECT file_id
FROM File
WHERE name = :fld))
ORDER BY score DESC