I have a SQL Server database table : History_KH
It look like:
Now I want to limit row number of this table (ex : 200 rows)
And when I insert new rows from code, It will insert on top of table. That's mean : Insert new rows on top of database table and the old rows over of 200 counts will be delete.
Please support me.
You can't really limit a table for a fix number of records but you can get rid of unwanted records. Assuming you are on SQL-Server
--STEP1 :Do your insert here
--STEP2: Delete older records over 200 ordering by dateTime column
;WITH CTE AS (
SELECT *, ROW_NUMBER() OVER (ORDER BY DateTime DESC) rn
FROM YourTable
)
DELETE CTE WHERE rn > 200
You didn't even post what database you are using. I'm assuming mysql.
Assuming you want to order by Datetime and Username is unique, use this update...
update `History_KH` set `Username` = $myUser, `Datetime` = $myDatetime,
`Datechange` = $myDatechange, `Value` = $myValue where `Username` in
(select `Username` from `History_KH` order by `Datetime` limit 200)
Related
There is a table with tow columns(ID, Data) and there are 3 rows with same value.
ID Data
4 192.168.0.22
4 192.168.0.22
4 192.168.0.22
Now I want to change third row DATA column. In update SQL Server Generate an error that I ca not change the value.
I can delete all 3 rows. But I can not delete third row separately.
This table is for a software that I bought and I changed the third Server IP.
You can try the following query
create table #tblSimilarValues(id int, ipaddress varchar(20))
insert into #tblSimilarValues values (4, '192.168.0.22'),
(4, '192.168.0.22'),(4, '192.168.0.22')
Use Below query if you want to change all rows
with oldData as (
select *,
count(*) over (partition by id, ipaddress) as cnt
from #tblSimilarValues
)
update oldData
set ipaddress = '192.168.0.22_1'
where cnt > 1;
select * from #tblSimilarValues
Use Below query if you want to skip firs row
;with oldData as (
select *,
ROW_NUMBER () over (partition by id, ipaddress order by id, ipaddress) as cnt
from #tblSimilarValues
)
update oldData
set ipaddress = '192.168.0.22_2'
where cnt > 1;
select * from #tblSimilarValues
drop table #tblSimilarValues
You can find the live demo live demo here
Since there is no column that allows us to distinguish these rows from each other, there's no "third row" (nor a first or second one for that matter).
We can use a ROW_NUMBER function to apply arbitrary row numbers to these rows, however, and if we place that in a CTE, we can apply DELETE/UPDATE actions via the CTE and use the arbitrary row numbers:
declare #t table (ID int not null, Data varchar(15))
insert into #t(ID,Data) values
(4,'192.168.0.22'),
(4,'192.168.0.22'),
(4,'192.168.0.22')
;With ArbitraryAssignments as (
select *,ROW_NUMBER() OVER (PARTITION BY ID, Data ORDER BY Data) as rn
from #t
)
delete from ArbitraryAssignments where rn > 2
select * from #t
This produces two rows of output - one row was deleted.
Note that I say that the ROW_NUMBER is arbitrary. One of the expressions in both the PARTITION BY and ORDER BY clauses is the same. By definition, then, we know that no real ORDER is defined by this (because all rows within the same partition, by definition, have the same value for that expression).
In this case ID columns allows duplicate value which is wrong, ID should be unique.
Now what you can do is create a new column make that unique or Primary Key or change the duplicate values of ID column and make it Unique/Primary key.
Now as per your Unique key/Primary key you can update DATA column value by query as below:
UPDATE <Table Name>
SET DATA = 'new data'
WHERE ID = 3;
I am trying to list all the duplicate records in a table. This table does not have a Primary Key and has been specifically created only for creating a report to list out duplicates. It comprises of both unique and duplicate values.
The query I have so far is:
SELECT [OfficeCD]
,[NewID]
,[Year]
,[Type]
FROM [Test].[dbo].[Duplicates]
GROUP BY [OfficeCD]
,[NewID]
,[Year]
,[Type]
HAVING COUNT(*) > 1
This works right and gives me all the duplicates - that is the number of times it occurs.
But I want to display all the values in my report of all the columns. How can I do that without querying for each record separately?
For example:
Each table has 10 fields and [NewID] is the field which is occuring multiple times.I need to create a report with all the data in all the fields where newID has been duplicated.
Please help.
Thank you.
You need a subquery:
SELECT * FROM yourtable
WHERE NewID IN (
SELECT NewID FROM yourtable
GROUP BY OfficeCD,NewID,Year,Type
HAVING Count(*)>1
)
Additionally you might want to check your tags: You tagged mysql, but the Syntax lets me think you mean sql-server
Try this:
SELECT * FROM [Duplicates] WHERE NewID IN
(
SELECT [NewID] FROM [Duplicates] GROUP BY [NewID] HAVING COUNT(*) > 1
)
select d.*
from Duplicates d
inner join (
select NewID
from Duplicates
group by NewID
having COUNT(*) > 1
) dd on d.NewID = dd.NewID
This is a known question but the best solution I've found is something like:
SELECT TOP N *
FROM MyTable
ORDER BY Id DESC
I've a table with lots of rows. It is not a posibility to use that query because it takes lot of time. So how can I do to select last N rows without using ORDER BY?
EDIT
Sorry duplicated question of this one
You can get SQL server to select the last N rows with the following query:
select * from tbl_name order by id desc limit N;
I tested JonVD's code, but found it was very slow, 6s.
This code took 0s.
SELECT TOP(5) ORDERID, CUSTOMERID, OrderDate
FROM Orders where EmployeeID=5
Order By OrderDate DESC
You can do it by using the ROW NUMBER BY PARTITION Feature also. A great example can be found here:
I am using the Orders table of the Northwind database... Now let us retrieve the Last 5 orders placed by Employee 5:
SELECT ORDERID, CUSTOMERID, OrderDate
FROM
(
SELECT ROW_NUMBER() OVER (PARTITION BY EmployeeID ORDER BY OrderDate DESC) AS OrderedDate,*
FROM Orders
) as ordlist
WHERE ordlist.EmployeeID = 5
AND ordlist.OrderedDate <= 5
If you want to select last numbers of rows from a table.
Syntax will be like
select * from table_name except select top
(numbers of rows - how many rows you want)* from table_name
These statements work but differrent ways. thank you guys.
select * from Products except select top (77-10) * from Products
in this way you can get last 10 rows but order will show descnding way
select top 10 * from products
order by productId desc
select * from products
where productid in (select top 10 productID from products)
order by productID desc
select * from products where productID not in
(select top((select COUNT(*) from products ) -10 )productID from products)
First you most get record count from
Declare #TableRowsCount Int
select #TableRowsCount= COUNT(*) from <Your_Table>
And then :
In SQL Server 2012
SELECT *
FROM <Your_Table> As L
ORDER BY L.<your Field>
OFFSET <#TableRowsCount-#N> ROWS
FETCH NEXT #N ROWS ONLY;
In SQL Server 2008
SELECT *
FROM
(
SELECT ROW_NUMBER() OVER(ORDER BY ID) AS sequencenumber, *
FROM <Your_Table>
Order By <your Field>
) AS TempTable
WHERE sequencenumber > #TableRowsCount-#N
In a very general way and to support SQL server here is
SELECT TOP(N) *
FROM tbl_name
ORDER BY tbl_id DESC
and for the performance, it is not bad (less than one second for more than 10,000 records On Server machine)
Is "Id" indexed? If not, that's an important thing to do (I suspect it is already indexed).
Also, do you need to return ALL columns? You may be able to get a substantial improvement in speed if you only actually need a smaller subset of columns which can be FULLY catered for by the index on the ID column - e.g. if you have a NONCLUSTERED index on the Id column, with no other fields included in the index, then it would have to do a lookup on the clustered index to actually get the rest of the columns to return and that could be making up a lot of the cost of the query. If it's a CLUSTERED index, or a NONCLUSTERED index that includes all the other fields you want to return in the query, then you should be fine.
select * from (select top 6 * from vwTable order by Hours desc) T order by Hours
Here's something you can try without an order by but I think it requires that each row is unique. N is the number of rows you want, L is the number of rows in the table.
select * from tbl_name except select top L-N * from tbl_name
As noted before, which rows are returned is undefined.
EDIT: this is actually dog slow. Of no value really.
A technique I use to query the MOST RECENT rows in very large tables (100+ million or 1+ billion rows) is limiting the query to "reading" only the most recent "N" percentage of RECENT ROWS. This is real world applications, for example I do this for non-historic Recent Weather Data, or recent News feed searches or Recent GPS location data point data.
This is a huge performance improvement if you know for certain that your rows are in the most recent TOP 5% of the table for example. Such that even if there are indexes on the Tables, it further limits the possibilites to only 5% of rows in tables which have 100+ million or 1+ billion rows. This is especially the case when Older Data will require Physical Disk reads and not only Logical In Memory reads.
This is well more efficient than SELECT TOP | PERCENT | LIMIT as it does not select the rows, but merely limit the portion of the data to be searched.
DECLARE #RowIdTableA BIGINT
DECLARE #RowIdTableB BIGINT
DECLARE #TopPercent FLOAT
-- Given that there is an Sequential Identity Column
-- Limit query to only rows in the most recent TOP 5% of rows
SET #TopPercent = .05
SELECT #RowIdTableA = (MAX(TableAId) - (MAX(TableAId) * #TopPercent)) FROM TableA
SELECT #RowIdTableB = (MAX(TableBId) - (MAX(TableBId) * #TopPercent)) FROM TableB
SELECT *
FROM TableA a
INNER JOIN TableB b ON a.KeyId = b.KeyId
WHERE a.Id > #RowIdTableA AND b.Id > #RowIdTableB AND
a.SomeOtherCriteria = 'Whatever'
MS doesn't support LIMIT in t-sql. Most of the times i just get MAX(ID) and then subtract.
select * from ORDERS where ID >(select MAX(ID)-10 from ORDERS)
This will return less than 10 records when ID is not sequential.
This query returns last N rows in correct order, but it's performance is poor
select *
from (
select top N *
from TableName t
order by t.[Id] desc
) as temp
order by temp.[Id]
use desc with orderby at the end of the query to get the last values.
This may not be quite the right fit to the question, but…
OFFSET clause
The OFFSET number clause enables you to skip over a number of rows and then return rows after that.
That doc link is to Postgres; I don't know if this applies to Sybase/MS SQL Server.
DECLARE #MYVAR NVARCHAR(100)
DECLARE #step int
SET #step = 0;
DECLARE MYTESTCURSOR CURSOR
DYNAMIC
FOR
SELECT col FROM [dbo].[table]
OPEN MYTESTCURSOR
FETCH LAST FROM MYTESTCURSOR INTO #MYVAR
print #MYVAR;
WHILE #step < 10
BEGIN
FETCH PRIOR FROM MYTESTCURSOR INTO #MYVAR
print #MYVAR;
SET #step = #step + 1;
END
CLOSE MYTESTCURSOR
DEALLOCATE MYTESTCURSOR
In order to get the result in ascending order
SELECT n.*
FROM
(
SELECT *
FROM MyTable
ORDER BY id DESC
LIMIT N
) n
ORDER BY n.id ASC
I stumpled acros this issue while using SQL server
What i did to resolve it is order the results descending and giving row number to the results of that, After i filtered the results and turned them around again.
SELECT *
FROM (
SELECT *
,[rn] = ROW_NUMBER() OVER (ORDER BY [column] DESC)
FROM [table]
) A
WHERE A.[rn] < 3
ORDER BY [column] ASC
Easy copy paste answer
To display last 3 rows without using order by:
select * from Lms_Books_Details where Book_Code not in
(select top((select COUNT(*) from Lms_Books_Details ) -3 ) book_code from Lms_Books_Details)
Try using the EXCEPT syntax.
Something like this:
SELECT *
FROM clientDetails
EXCEPT
(SELECT TOP (numbers of rows - how many rows you want) *
FROM clientDetails)
I have a database with 1000 records.
I am trying to create an SQL statement so if the number of records grows above 1000, then the oldest records are deleted (i.e. the new records above 1000 'replace' the oldest records).
I am using SQLite, but I assume the usual SQL syntax will fit here.
If you use an auto-increment field, you can easily write this to delete the oldest 100 records:
DELETE FROM mytable WHERE id IN (SELECT id FROM mytable ORDER BY id ASC LIMIT 100)
Or, if no such field is present, use ROWID:
DELETE FROM mytable WHERE ROWID IN (SELECT ROWID FROM mytable ORDER BY ROWID ASC LIMIT 100)
Or, to leave only the latest 1000 records:
DELETE FROM mytable WHERE ROWID IN (SELECT ROWID FROM mytable ORDER BY ROWID DESC LIMIT -1 OFFSET 1000)
Assuming that your table has a Primary Key and a column with a timestamp indicating when the record was inserted), you can use a query along the lines of
delete from tableToDeleteFrom
where tablePK in
(select tablePK
from tableToDeleteFrom
where someThresholdDate <= #someThresholdDate)
For delete all records except the first record (min/max id) you can use:
SET #ls AS INT
SELECT #ls = MIN(id) FROM DATA
DELETE FROM DATA WHERE id <> #ls
Can somebody please, help me with a query to delete only 500 rows from a table which has 20000 rows. Also has to be older than a particular date.
Thanks for your help,
Soofy
You can use the Top keyword like you would in a select
Delete Top (500)
From myTable
Where Date < '01/01/2009'
If you're using SQL Server 2005, you can do this:
DELETE TOP (500) FROM your_table
WHERE date_field < #my_particular_date
or you can do this:
SET ROWCOUNT 500
DELETE your_table
WHERE date_field < #my_particular_date
in SQL Server 2000, you can do this:
DELETE your_table
WHERE pk_field IN (
SELECT TOP (500) * FROM your_table
WHERE date_field < #my_particular_date
)
DELETE FROM Table_Name WHERE Primary_Key_Column IN (
SELECT TOP 500 Primary_Key_Column FROM Table_Name WHERE [Date] < '01/01/2009' ORDER BY Primary_Key_Column ASC
)
SET ROWCOUNT 500
DELETE FROM TableName WHERE TheDate < #YourDate
Top only works in Transact Sql, each sql has it's own version
For mySql and posGres
Delete
From myTable
Where Date < '01/01/2009'
LIMIT 10;
For oracle:
SELECT
FROM myTable
WHERE Date < '01/01/2009'
and ROWNUM <= 10
The only thing I'll add is you probably want to use "ORDER BY [DATE] DESC" at the end of most of these queries. And if you have multiple matching dates, you'll want to add additional column ordering to get the correct values deleted.
This presumes of course, that you actually have a "createddate" or "modifieddate" you can use to sort by. You didn't specify whether it was the oldest created or the oldest unmodified. (ie if ID=1 is the oldest but I modified it yesterday should it still be deleted?) which you'll need to be careful with if you sort by the primary key - assuming you're using an incrementing primary key and not GUIDs or something...