Amateur SQL writer here having a problem with building out table based on values from an existing one.
The MASTER table logs a record with an ID every time a service is used. ID remains the same per user, but will repeat to track relevant information during that usage. Table holds about 2m records and 20k DISTINCT IDs.
*Example -
USER ID | Used_Amount
USER_1998 | 9GB,
USER_1999 | 4GB,
USER_1999 | 1GB,
USER_1999 |0.5 GB*
Would like for the new table is create column that SUMS the usage and organizes based on DISTINCT ID.
Goal -
ID . TOTAL USAGE
USER_1998 - 9GB
USER_1999 - 5.5GB
Code below is my attempt...
UPDATE ml_draft
SET true_usage = (
SELECT SUM(true_usage)
FROM table2 t2
INNER JOIN ml_draft ON
ml_draft.subscription_id = t2.subscription_id);
Let me know if there are any additional details to add. Errors vary
You want a correlated subquery. So, there is no need to use JOIN in the subquery:
UPDATE ml_draft d
SET true_usage = (SELECT SUM(t2.true_usage)
FROM table2 t2
WHERE d.subscription_id = t2.subscription_id
);
For performance, you want an index on table2(subscription_id, true_usage).
Related
Good evening everyone, I'm trying to do an update on a Table but I can't really make it work
The feature needed is:
-Watch a field on a form, it contains the number of people that need to sit at the restaurant table.
-Find the first free table that has enough seats, set it as busy and assign a random waiter
Any idea?
more db infos:
Table "Waiters" is composed by ID(Autonumber),Name(Short Text). Has 2 names atm
Table "Tables" is composed by ID(Autonumber),Seats(Number),Busy(y/n),Waiter(short text). All tables have a fixed number of seats and have no Waiter + not busy
SOLUTION:
In the end i used "First" for the assignment and it works perfectly as it follows:
UPDATE Tables SET Tables.Waiter = DLookUp("FirstName","TopWtr")
WHERE ID IN (SELECT FIRST (ID)
FROM Tables
WHERE Seats >= Val(Forms!Room!Text12) AND Waiter Is Null);
Top wasn't working because it was returning multiple records - every table with same number of seats - and couldn't make it work with DISTINCT. This works probably because the table is already ordered by seats
Thanks to June7 for the input
Cannot SET a field value to result of a SELECT subquery - SELECT returns a dataset not a single value. Can return a single value with domain aggregate function.
Build a query object named TopWtr:
SELECT Top 1 ID FROM Waiters ORDER BY Rnd(ID);
Then use DLookup to pull that value. The Busy field seems redundant because if table has a waiter assigned that would indicate busy.
UPDATE Tables SET Tables.Waiter = DLookUp("ID","TopWtr"), Tables.Busy = True
WHERE ID IN (SELECT TOP 1 ID FROM Tables
WHERE Seats >= Val(Forms!Room!Testo17) AND Waiter Is Null
ORDER BY Seats)
An INNER JOIN may be preferable to WHERE clause:
UPDATE Tables INNER JOIN (SELECT TOP 1 ID FROM Tables
WHERE Seats >= Val(Forms!Room!Testo17) AND Waiter Is Null
ORDER BY Seats) AS T1
ON Tables.ID = T1.ID
SET Tables.Waiter = DLookUp("ID","TopWtr"), Tables.Busy = True
Please who can help with this scenario?
I have two tables, both they have a common column ID, and Table 1 has a column Title. Normally I should update the content of this Title column for some ID, but since the table was already in use somewhere else, it wasn't a good idea to change data directly in Table 1.
That's why I created a new table table 2, which hold only the Title that must be changed associated with these ID that must be changed.
Now I am trying to get these updated titles from table 2, when there is a matching ID in table 1, otherwise show only the contents of table 1.
The result should be something like that but without using If statements.
__ID__ Title
| | | |
| | | |
You can use LEFT OUTER JOIN to this new table and COALESCE() function to say "If there is data in the new table, use it, otherwise use the data in the existing table" . Something like:
SELECT t1.id, COALESCE(t2.title, t1.title) as title
FROM t1
LEFT OUTER JOIN t2 ON t1.id = t2.id;
Good Day,
I have 3 Tables - Ticket, Ticket Batch (Multiple Ticket Rows To One Batch) and Ticket Staff (Multiple Staff Rows To One Ticket) and wish to ultimately UPDATE the ticket_batch table with the COUNT of all staff working on tickets per ticket batch.
The tables with applicable columns look as follows
ticket:
| ticket_number | recon_number |
ticket_batch:
| recon_number |
ticket_staff:
| ticket_number |
So I have written the following SQL query to essentially first if I do get the COUNT:
SELECT COUNT(*)
FROM ticket_staf
WHERE ticket_staff.ticket_number IN (SELECT GROUP_CONCAT(ticket.ticket_number) FROM ticket WHERE ticket.recon_number = 1);
Which the query just keeps running, but when I execute the queries separately:
SELECT GROUP_CONCAT(ticket.ticket_number)
FROM ticket
WHERE ticket.recon_number = 1;
I get 5 ticket numbers within split seconds and if I paste that string in the other portion of the query:
SELECT COUNT(*)
FROM ticket_staff
WHERE ticket_staff.ticket_number IN (1451,1453,1968,4457,4458);
It returns the correct COUNT.
So ultimately I guess can I not write queries with GROUP_CONCATS into another SELECT WHERE IN? And how should I structure my query?
Thanks for reading :)
I prefer Inner join as follows:
SELECT COUNT(distinct ts.*)
FROM ticket_staff ts
LEFT JOIN ticket t
ON ts.ticket_number = t.ticket_number
WHERE t.recon_number = 1;
GROUP_CONCAT() doesn't look right. I suspect you are confusing a list of values for IN with a string. They are not the same thing.
In general, I would recommend EXISTS over IN anyway:
SELECT COUNT(*)
FROM ticket_staff ts
WHERE EXISTS (SELECT 1
FROM ticket t
WHERE ts.ticket_number = t.ticket_number AND
t.recon_number = 1
);
For this query, you want an index on ticket(ticket_number, recon_number). However, I am guessing that ticket(ticket_number) is the primary key, which is enough of an index by itself.
I have two tables which are joined by an ID...
table 1
- Assessment ID
- Module ID
- Assessment Weighting
table 2
- ID
- AssessmentID
- ModuleID
- UserID
- MarkFrom100
An assessment can have many students taking the assessment.
For example
A module has two assessments, one worth 60% and the other worth 40%. in table 2, I want to take the weighting value from table 1 and multiply it against the mark from 100.
SELECT * FROM Assessment, ModuleAssessmentUser WHERE
INNER JOIN moduleassementuser.assessmentID on Assessment.assessmentID
MULTIPLY AssessmentWeighting BY MarkFrom100 AS finalmark
UserID = 1
I know this is way off, but I really don't know how else to go about it.
My SQL knowledge is limited, so any help is appreciated!
You may use a SUM function in your query which will sum all the data of a certain group in a sub query wich will allow you to multiply the sum to the weight
sub query :
SELECT ModuleID, AssessmentID, UserID, SUM(MarkFrom100) as Total
FROM Table_2
GROUP BY ModuleID
Then use this sub query as a table in a main query :
SELECT T1.Assessment_ID, T1.ModuleID, Q1.UserID (Q1.Total * T1.Assessment_Weighting) as FinalMark
FROM (SELECT ModuleID, UserID, SUM(MarkFrom100) as Total
FROM Table_2
GROUP BY ModuleID) AS Q1
INNER JOIN Table_1 as T1 on T1.ModuleID = Q1.ModuleID
-- WHERE T1.ModuleID = 2 -- a particular module ID
GROUP BY ModuleID;
Note that the WHERE statement is in comment. If you want the whole data, remove it, if you want a particular data, use it ^^
NOTE :
I don't have your database, so it may need some tweeks, but the main idea is there
I have tables with multiple million rows and need to fetch the last rows of specific ID's
for example the last row which has device_id = 123 AND the last row which has device_id = 1234
because the tables are so huge and ordering takes so much time, is it possible to select the last 200 without ordering the table and then just order those 200 and fetch the rows I need.
How would I do that?
Thank you in advance for your help!
UPDATE
My PostgreSQL version is 9.2.1
sample data:
time device_id data data ....
"2013-03-23 03:58:00-04" | "001EC60018E36" | 66819.59 | 4.203
"2013-03-23 03:59:00-04" | "001EC60018E37" | 64277.22 | 4.234
"2013-03-23 03:59:00-04" | "001EC60018E23" | 46841.75 | 2.141
"2013-03-23 04:00:00-04" | "001EC60018E21" | 69697.38 | 4.906
"2013-03-23 04:00:00-04" | "001EC600192524"| 69452.69 | 2.844
"2013-03-23 04:01:00-04" | "001EC60018E21" | 69697.47 | 5.156
....
See SQLFiddle of this data
So if device_id = 001EC60018E21
I would want the most recent row with that device_id.
It is a grantee that the last row with that device_id is the row I want, but it may or may not be the last row of the table.
Personally I'd create a composite index on device_id and descending time:
CREATE INDEX table1_deviceid_time ON table1("device_id","time" DESC);
then I'd use a subquery to find the highest time for each device_id and join the subquery results against the main table on device_id and time to find the relevant data, eg:
SELECT t1."device_id", t1."time", t1."data", t1."data1"
FROM Table1 t1
INNER JOIN (
SELECT t1b."device_id", max(t1b."time") FROM Table1 t1b GROUP BY t1b."device_id"
) last_ids("device_id","time")
ON (t1."device_id" = last_ids."device_id"
AND t1."time" = last_ids."time");
See this SQLFiddle.
It might be helpful to maintain a trigger-based materialized view of the highest timestamp for each device ID. However, this will cause concurrency issues if most than one connection can insert data for a given device ID due to the connections fighting for update locks. It's also a pain if you don't know when new device IDs will appear as you have to do an upsert - something that's very inefficient and clumsy. Additionally, the extra write load and autovacuum work created by the summary table may not be worth it; it might be better to just pay the price of the more expensive query.
BTW, time is a terrible name for a column because it's a built-in data type name. Use something more appropriate if you can.
The general way to get the "last" row for each device_id looks like this.
select *
from Table1
inner join (select device_id, max(time) max_time
from Table1
group by device_id) T2
on Table1.device_id = T2.device_id
and Table1.time = T2.max_time;
Getting the "last" 200 device_id numbers without using an ORDER BY isn't really practical, but it's not clear why you might want to do that in the first place. If 200 is an arbitrary number, then you can get better performance by taking a subset of the table that's based on an arbitrary time instead.
select *
from Table1
inner join (select device_id, max(time) max_time
from Table1
where time > '2013-03-23 12:03'
group by device_id) T2
on Table1.device_id = T2.device_id
and Table1.time = T2.max_time;