I am using SQL Server Compact 4.0 and am trying to get one query to return a single record with a column Alarm based on the maximum identity when another column Cleared is NULL.
This works:
SELECT Id, Alarm
FROM Alarm_History
WHERE Cleared IS NULL
Giving me half the answer. The problem is that it returns several records.
This also works:
SELECT MAX(Id)
FROM Alarm_History
WHERE Cleared IS NULL
And it gives me the other half of the answer, but I can't get the value "Alarm" that I am looking for.
But they DON'T work together as in:
SELECT Id, Alarm
FROM Alarm_History
WHERE Cleared IS NULL AND Id = MAX(Id)
OR
SELECT MAX(Id), Alarm
FROM Alarm_History
WHERE Cleared IS NULL
With the queries above I can do two consecutive queries to get the result back, but I don't think this is very efficient. Is there a way to do this in one trip to the database?
Thanks
Jeff
You could do it with max and a join, but that would be far too complicated. Instead, you can just try:
SELECT TOP 1 Id, Alarm
FROM Alarm_History
WHERE Cleared IS NULL
ORDER BY Id DESC
Note: what happens if two alarms have max id ? Well, that shouldn't happen (Id is unique). But that's an interesting problem nevertheless (suppose the field is not Id but Price, and you want all alarms with max price, and you don't know how many there'll be, so you cannot use TOP 1 anymore).
You'll have to use a CROSS JOIN;
SELECT Id, Price
FROM Alarms
JOIN (SELECT MAX(Price) as maxPrice FROM Alarms) b
WHERE Alarms.Price = b.maxPrice
Don't think "max". Think "order by". Try this:
SELECT TOP 1 Id, Alarm
FROM Alarm_History
WHERE Cleared IS NULL
ORDER BY Id DESC;
That way, you can get all the fields you want associated with the max id.
Try,
SELECT Id, Alarm FROM Alarm_History WHERE ID in (SELECT MAX(Id) FROM Alarm_History WHERE Cleared IS NULL)
Related
Let's say I have a table like so
CREATE TABLE Records (Event VARCHAR, Severity INT, Location VARCHAR)
I'd like to be able to grab the Event name and location of the row with the lowest severity. How could I achieve this?
Using top(1), limit(1) etc... you will get only one record with the lowest severity, but in case there are 2 of them you will lose the second.
I suggest you to use a nested query as follows:
from records r
where Severity = (
select min(severity)
from records
)
One simple method:
select top (1) r.*
from records r
order by r.severity;
If you want all rows in the event of ties, then use:
select top (1) with ties r.*
Failed finding a solution to my problem, would love your help.
~~ Post has been edited to have only one question ~~-
Group by one query while selecting multiple columns.
In MySQL you can simply group by whatever you want, and it will still select all of them, so if for example I wanted to select the newest 100 transactions, grouped by Email (only get the last transaction of a single email)
In MySQL I would do that:
SELECT * FROM db.transactionlog
group by Email
order by TransactionLogId desc
LIMIT 100;
In SQL Server its not possible, googling a bit suggested to specify each column that I want to have with an aggregate as a hack, that couldn't cause a mix of values (mixing columns between the grouped rows)?
For example:
SELECT TOP(100)
Email,
MAX(ResultCode) as 'ResultCode',
MAX(Amount) as 'Amount',
MAX(TransactionLogId) as 'TransactionLogId'
FROM [db].[dbo].[transactionlog]
group by Email
order by TransactionLogId desc
TransactionLogId is the primarykey which is identity , ordering by it to achieve the last inserted.
Just want to know that the ResultCode and Amount that I'll get doing such query will be of the last inserted row, and not the highest of the grouped rows or w/e.
~Edit~
Sample data -
row1:
Email : test#email.com
ResultCode : 100
Amount : 27
TransactionLogId : 1
row2:
Email: test#email.com
ResultCode:50
Amount: 10
TransactionLogId: 2
Using the sample data above, my goal is to get the row details of
TransactionLogId = 2.
but what actual happens is that I get a mixed values of the two, as I do get transactionLogId = 2, but the resultcode and amount of the first row.
How do I avoid that?
Thanks.
You should first find out which is the latest transaction log by each email, then join back against the same table to retrieve the full record:
;WITH MaxTransactionByEmail AS
(
SELECT
Email,
MAX(TransactionLogId) as LatestTransactionLogId
FROM
[db].[dbo].[transactionlog]
group by
Email
)
SELECT
T.*
FROM
[db].[dbo].[transactionlog] AS T
INNER JOIN MaxTransactionByEmail AS M ON T.TransactionLogId = M.LatestTransactionLogId
You are currently getting mixed results because your aggregate functions like MAX() is considering all rows that correspond to a particular value of Email. So the MAX() value for the Amount column between values 10 and 27 is 27, even if the transaction log id is lower.
Another solution is using a ROW_NUMBER() window function to get a row-ranking by each Email, then just picking the first row:
;WITH TransactionsRanking AS
(
SELECT
T.*,
MostRecentTransactionLogRanking = ROW_NUMBER() OVER (
PARTITION BY
T.Email -- Start a different ranking for each different value of Email
ORDER BY
T.TransactionLogId DESC) -- Order the rows by the TransactionLogID descending
FROM
[db].[dbo].[transactionlog] AS T
)
SELECT
T.*
FROM
TransactionsRanking AS T
WHERE
T.MostRecentTransactionLogRanking = 1
can someone help me about counting rows in sql. I have a table, archive, in which I have bank account and status of that account. One account can have and usually have more records, in my count I have to use last record, not records before. Example:
account status
5552222 A
5552222 B
5552222 A
**5552222 B**
4445896 A
4445896 B
**4445896 A**
I have to use this who are bold. Based on this there is one B(blocked) and one A(active) account. I have column datetime, which can tell me what is last record. I just need query to count that
Assuming you want to count based on the most current row for an account:
SELECT tab.status,
COUNT(*)
FROM tab JOIN
(
SELECT account, MAX(datetime) AS maxdate
FROM tab
GROUP BY account
) AS dt
ON tab.account = dt.account
AND tab.datetime = dt.maxtime
GROUP BY tab.Status
SELECT COUNT(*)
FROM yourTable
WHERE Status='B'
or
WHERE AccountName LIKE '%B'
Edit: After OP modified the question to include the table data.
So, the problem is that the same account number can occur multiple times, and you want to count on the basis of last status of the account.
If the account is currently blocked, you would like to count it, irrespective of the number of times it gets blocked earlier.
Assumption: You have a date type column in your table which shows the date when the record's (with new status value) was inserted (or it may be an identity field which keeps track of the order of records created in the table)
The query will be:
SELECT COUNT (*)
FROM
(
SELECT DISTINCT
acNumber,
( SELECT Max(identityField_or_dateField)
FROM tableName t
WHERE t.acNumber = t2.acNumber AND Status='B')
FROM tableName t2
WHERE
( SELECT Max(identityField_or_dateField)
FROM tableName t
WHERE t.acNumber = t2.acNumber AND Status='B') IS NOT NULL
) tblAlias
Glad to help! Please remember to accept the answer if you found it helpful.
I'm building a BI report for a client where there is a 1-n related join involved.
The joined table has a field for employee ID (EmplId).
The query that I've built for this report is supposed to give a 1 in its field "OneEmployee" if all the related posts have the same employee in the EmplId field, null if it's different employees, i.e:
TaskTrans
TaskTransHours > EmplId: 'John'
TaskTransHours > EmplId: 'John'
This should give a 1 in the said field in the query
TaskTrans
TaskTransHours > EmplId: 'John'
TaskTransHours > EmplId: 'George'
This should leave the said field blank
The idea is to create a field where a case function checks this and returns the correct value. But my problem is whereas there is a way to check for this through SQL.
select not count(*) from your_table
where employee_id = GIVEN_ID
and your_field not in ( select min(your_field)
from your_table
where employee_id = GIVEN_ID);
Note: my first idea was to use LIMIT 1 in the inner query, but MYSQL didn't like it, so min it was - the points to use any, but only one. Min should work, but the field should be indexed, then this query will actually execute rather fast, as only indexes would be used (obviously employee_id should also be indexed).
Note2: Do not get too confused with not in front of count(*), you want 1 when there is none that is different, I count different ones, and then give you the not count(*), which will be one if count is 0, otherwise 0.
Seems a job for a window COUNT():
SELECT
…,
CASE COUNT(DISTINCT TaskTransHours.EmplId) OVER () WHEN 1 THEN 1 END
AS OneEmployee
FROM …
i have loanTable that contain two field loan_id and status
loan_id status
==============
1 0
2 9
1 6
5 3
4 5
1 4 <-- How do I select this??
4 6
In this Situation i need to show the last Status of loan_id 1 i.e is status 4. Can please help me in this query.
Since the 'last' row for ID 1 is neither the minimum nor the maximum, you are living in a state of mild confusion. Rows in a table have no order. So, you should be providing another column, possibly the date/time when each row is inserted, to provide the sequencing of the data. Another option could be a separate, automatically incremented column which records the sequence in which the rows are inserted. Then the query can be written.
If the extra column is called status_id, then you could write:
SELECT L1.*
FROM LoanTable AS L1
WHERE L1.Status_ID = (SELECT MAX(Status_ID)
FROM LoanTable AS L2
WHERE L2.Loan_ID = 1);
(The table aliases L1 and L2 could be omitted without confusing the DBMS or experienced SQL programmers.)
As it stands, there is no reliable way of knowing which is the last row, so your query is unanswerable.
Does your table happen to have a primary id or a timestamp? If not then what you want is not really possible.
If yes then:
SELECT TOP 1 status
FROM loanTable
WHERE loan_id = 1
ORDER BY primaryId DESC
-- or
-- ORDER BY yourTimestamp DESC
I assume that with "last status" you mean the record that was inserted most recently? AFAIK there is no way to make such a query unless you add timestamp into your table where you store the date and time when the record was added. RDBMS don't keep any internal order of the records.
But if last = last inserted, that's not possible for current schema, until a PK addition:
select top 1 status, loan_id
from loanTable
where loan_id = 1
order by id desc -- PK
Use a data reader. When it exits the while loop it will be on the last row. As the other posters stated unless you put a sort on the query, the row order could change. Even if there is a clustered index on the table it might not return the rows in that order (without a sort on the clustered index).
SqlDataReader rdr = SQLcmd.ExecuteReader();
while (rdr.Read())
{
}
string lastVal = rdr[0].ToString()
rdr.Close();
You could also use a ROW_NUMBER() but that requires a sort and you cannot use ROW_NUMBER() directly in the Where. But you can fool it by creating a derived table. The rdr solution above is faster.
In oracle database this is very simple.
select * from (select * from loanTable order by rownum desc) where rownum=1
Hi if this has not been solved yet.
To get the last record for any field from a table the easiest way would be to add an ID to each record say pID. Also say that in your table you would like to hhet the last record for each 'Name', run the simple query
SELECT Name, MAX(pID) as LastID
INTO [TableName]
FROM [YourTableName]
GROUP BY [Name]/[Any other field you would like your last records to appear by]
You should now have a table containing the Names in one column and the last available ID for that Name.
Now you can use a join to get the other details from your primary table, say this is some price or date then run the following:
SELECT a.*,b.Price/b.date/b.[Whatever other field you want]
FROM [TableName] a LEFT JOIN [YourTableName]
ON a.Name = b.Name and a.LastID = b.pID
This should then give you the last records for each Name, for the first record run the same queries as above just replace the Max by Min above.
This should be easy to follow and should run quicker as well
If you don't have any identifying columns you could use to get the insert order. You can always do it like this. But it's hacky, and not very pretty.
select
t.row1,
t.row2,
ROW_NUMBER() OVER (ORDER BY t.[count]) AS rownum from (
select
tab.row1,
tab.row2,
1 as [count]
from table tab) t
So basically you get the 'natural order' if you can call it that, and add some column with all the same data. This can be used to sort by the 'natural order', giving you an opportunity to place a row number column on the next query.
Personally, if the system you are using hasn't got a time stamp/identity column, and the current users are using the 'natural order', I would quickly add a column and use this query to create some sort of time stamp/incremental key. Rather than risking having some automation mechanism change the 'natural order', breaking the data needed.
I think this code may help you:
WITH cte_Loans
AS
(
SELECT LoanID
,[Status]
,ROW_NUMBER() OVER(ORDER BY (SELECT 1)) AS RN
FROM LoanTable
)
SELECT LoanID
,[Status]
FROM LoanTable L1
WHERE RN = ( SELECT max(RN)
FROM LoanTable L2
WHERE L2.LoanID = L1.LoanID)