For a very simple query:
List list = await mydb.rawQuery('SELECT COUNT(1) as tot FROM myTable')
list returns [{tot: 541}]
How can I get the value 541 in a simple way without creating a class?
Related
I wish to know how I can use postgres returning clause with SQL Boiler elegantly.
For example I wish to update some object by some fields and return the object id:
err = queries.RawG(`update users
set name='test-name'
WHERE email='test#example.com'
RETURNING id`).Bind(ctx, boil.GetDB(), &user)
The following is working as expected, the user column has been updated and I got back the user id, but I'm looking for more elegant ways to do the same without using queries.RawG
I'm trying to get the count of events in a ksqlDB table within an arbitrary time window.
The table my_table was created with a WINDOW SESSION.
It is important to note the query is being run after all data was processed, and the ksqlDB server is basically doing nothing.
My query looks something like this
count(*) as count
FROM my_table
WHERE WINDOWSTART < (1602010972370 + 5000) AND WINDOWEND > 1602010972370
group by 1 emit changes;
Running this kind of query will very often return one result row, and immediately after a second result row with the actual "final" result.
It doesn't look like its a result of values in the table not being "settled" yet, because if I repeat the same query (as many times as I want) I get the same exact behavior.
I'm assuming there is some configuration value which will let ksqlDB to wait just a little longer (in the order of one second) before it returns the result, so I could get the final result in the first row?
BTW using emit final will not work on the query itself since it only apply to "windowed querys"
I have a simple reporting query group by id and day that looks like the following:
select id,
avg(case when name = 'temp' then value end) as average_temp,
DATE_TRUNC('day', timestamp) as day
from data
group by id, day
order by id;
The query basically needs to show the average daily temperature for each asset.
The user is able to specify a bunch of different aggregation functions beyond just 'average', the above is only a simple example. For example, avg temp, max temp, max speed, etc.
I'm trying to translate that into JPA as follows:
CriteriaQuery<Object[]> query = criteriaBuilder.createQuery(Object[].class);
Root<AssetMetricDataPoint> root = query.from(Data.class);
List<Selection<?>> selectionList = getSelections(aggregationQuery, criteriaBuilder, root);
Expression<Instant> groupDate = criteriaBuilder.function("date_trunc", Instant.class, criteriaBuilder.literal("day"), root.get("timestamp"));
selectionList.add(groupDate.alias("day"));
query.multiselect(selectionList);
query.where(getWherePredicates(aggregationQuery, criteriaBuilder, root));
query.orderBy(getOrderBy(aggregationQuery, criteriaBuilder, root));
query.groupBy(root.get("id"), groupDate);
return this.setupPagination(entityManager.createQuery(query), aggregationQuery);
I'm using criteriaBuilder.function to group by the date. However, when I execute the query using JPA I get the following exception:
org.postgresql.util.PSQLException: ERROR: column "data0_.timestamp" must appear in the GROUP BY clause or be used in an aggregate function
This appears to occur because the query is parametized and Postgres doesn't realize that the 'day' parameter that appears in both the select and group by clauses are the same.
Is there any way around this. Can I somehow bake in the 'day' value so it's not sent a parameter? Or some other method?
In the end there's a relatively solution to the problem. Rather than grouping by the expression, I thought I'd try to group by the alias instead: criteriaBuilder.literal("day"). This didn't work, however, with Postgres complaining about a non-integer literal.
I then realised I could group by a positional integer instead, which in my case ended up looking like:
query.groupBy(root.get("id"), criteriaBuilder.literal(selectionList.size()));
This works as expected.
I have PostgreSQL query where I need to return vehicleId, plateNumber and one last "position" data in order to see where the vehicle stopped. I have three tables. Vehicle table, session table storing the sessions and tracking table storing the actual position data of the vehicle.
Getting the plateNumber and vehicleId does work, however adding the position and trying to group the results will end with the following error: ERROR: could not identify an equality operator for type JSON.
Is there any way around this. How could I force (convert the JSON) so it can be actually measured? The JSON contains position data from the mobile which seem to be having a unified structure. There is timestamp, lat, long, speed and heading.
Alternatively is there any other way the query could be written as not to involve the need to compare the JSON data? Any recommendation? I have tried a few different approaches with no result. I always seem to hit the issue with the JSON.
SELECT "plateNumber", "Config.Vehicle"."vehicleId", position
FROM "Config.Vehicle"
INNER JOIN "Config.Session" ON "Config.Session"."vehicleId" = "Config.Vehicle"."vehicleId"
LEFT JOIN (select * from "Config.Tracking" ORDER BY date DESC LIMIT 1) a ON a."sessionId" = "Config.Session"."sessionId"
WHERE "Config.Session"."sessionEnd" IS NOT NULL
GROUP BY 1, 2, 3
I have 2 SQL Server databases, hosted on two different servers. I need to extract data from the first database. Which is going to be a list of integers. Then I need to compare this list against data in multiple tables in the second database. Depending on some conditions, I need to update or insert some records in the second database.
My solution:
(WCF Service/Entity Framework using LINQ to Entities)
Get the list of integers from 1st db, takes less than a second gets 20,942 records
I use the list of integers to compare against table in the second db using the following query:
List<int> pastDueAccts; //Assuming this is the list from Step#1
var matchedAccts = from acct in context.AmAccounts
where pastDueAccts.Contains(acct.ARNumber)
select acct;
This above query is taking so long that it gives a timeout error. Even though the AmAccount table only has ~400 records.
After I get these matchedAccts, I need to update or insert records in a separate table in the second db.
Can someone help me, how I can do step#2 more efficiently? I think the Contains function makes it slow. I tried brute force too, by putting a foreach loop in which I extract one record at a time and do the comparison. Still takes too long and gives timeout error. The database server shows only 30% of the memory has been used.
Profile the sql query being sent to the database by using SQL Profiler. Capture the SQL statement sent to the database and run it in SSMS. You should be able to capture the overhead imposed by Entity Framework at this point. Can you paste the SQL Statement emitted in step #2 in your question?
The query itself is going to have all 20,942 integers in it.
If your AmAccount table will always have a low number of records like that, you could just return the entire list of ARNumbers, compare them to the list, then be specific about which records to return:
List<int> pastDueAccts; //Assuming this is the list from Step#1
List<int> amAcctNumbers = from acct in context.AmAccounts
select acct.ARNumber
//Get a list of integers that are in both lists
var pastDueAmAcctNumbers = pastDueAccts.Intersect(amAcctNumbers);
var pastDueAmAccts = from acct in context.AmAccounts
where pastDueAmAcctNumbers.Contains(acct.ARNumber)
select acct;
You'll still have to worry about how many ids you are supplying to that query, and you might end up needing to retrieve them in batches.
UPDATE
Hopefully somebody has a better answer than this, but with so many records and doing this purely in EF, you could try batching it like I stated earlier:
//Suggest disabling auto detect changes
//Otherwise you will probably have some serious memory issues
//With 2MM+ records
context.Configuration.AutoDetectChangesEnabled = false;
List<int> pastDueAccts; //Assuming this is the list from Step#1
const int batchSize = 100;
for (int i = 0; i < pastDueAccts.Count; i += batchSize)
{
var batch = pastDueAccts.GetRange(i, batchSize);
var pastDueAmAccts = from acct in context.AmAccounts
where batch.Contains(acct.ARNumber)
select acct;
}