I have the following SQL view:
CREATE VIEW [dbo].[VW_ScanData]
AS
SELECT
top 10 ID,
Chip_ID,
[IPAddress] As FilterKey,
[DateTime]
FROM
TBL_ScanData WITH(NOLOCK)
ORDER BY ID DESC
GO
The idea is that this returns the 10 most recent entries. I have been told to to use a filterkey to check recent entries per IP Address.
The problem is that as it stands above, it will return the top 10 entries and remove all the ones that dont match the filter key which means in some cases it will not return anything.
I want it to return the 10 most recent entries of the given IP Address (Filter key).
I have tried removing 'top 10', but it will then not accept the order by clause, meaning it will not necessarily give the most recent entries.
As said, I need to use a filter key to comply with the rest of the framework of the project
I would recommend that you do not bake concerns like row limits, ordering, and lock hints into a view, as this will limit the usefulness / reusability of the view to different consumers. Instead, leave it up to the caller to decide on such concerns, which can be applied retrospectively when using the view.
If you remove the row limit from the view, filter and row limit can then be done from the caller:
SELECT TOP 10 *
FROM [dbo].[VW_ScanData]
WHERE FilterKey = 'FOO'
ORDER BY ID DESC;
That said, the view then doesn't really add any value beyond selecting from the table directly, other than the aliasing of IPAddress:
CREATE VIEW [dbo].[VW_ScanData]
AS
SELECT
ID,
Chip_ID,
[IPAddress] As FilterKey,
[DateTime]
FROM
TBL_ScanData
GO
Edit
Other options available to you are using a stored procedure or a Table user defined function. The latter will allow you to bake in all the concerns you require, and the Filter key can be passed as a parameter to the function:
CREATE FUNCTION [dbo].[FN_ScanData](#FilterKey VARCHAR(50))
RETURNS #Result TABLE
(
ID INT,
Chip_ID INT,
FilterKey VARCHAR(50),
[DateTime] DATETIME
)
AS
BEGIN
INSERT INTO #Result
SELECT
top 10 ID,
Chip_ID,
[IPAddress] As FilterKey,
[DateTime]
FROM
TBL_ScanData WITH(NOLOCK) -- This will bite you!
WHERE
[IPAddress] = #FilterKey
ORDER BY ID DESC
RETURN
END
Which you can then call like so ('Foo' is your filter key):
SELECT *
FROM [dbo].[FN_ScanData]('FOO');
This select gets the last 10 entries per FilterKey.
select id,chip_id,FilterKey,[DateTime]
FROM (SELECT ID,
Chip_ID,
FilterKey,
[DateTime],
ROW_NUMBER() OVER (Partition By FilterKey Order BY ID DESC) AS RN
FROM TBL_ScanData WITH(NOLOCK) )
WHERE RN <= 10
Related
I have a logging table that is live which saves my value to a table frequently.
My plan is to take those values and put them on a temporary table with
SELECT * INTO #temp from Block
From there I guess my block table is empty and the logger can keep on logging new values.
The next step is that I want to save them in a existing table. I wanted to use
INSERT INTO TABLENAME(COLUMN1,COLUMN2...) SELECT (COLUMN1,COLUMN2...) FROM #temp
The problem is that the #temp table has duplicates primary keys. And I only want to store the last ID.
I have tried DISTINCT but it didn't work. Could not get ROW_Count to work. Are there any ideas on how I should do it? I wish to make it with as few reads as possible.
Also, in the future I plan to send them to another database, how do I do that on SQL Server? I guess it's something like FROM Table [in databes]?
I couldn't get the blocks to copy. But here goes:
create TABLE Product_log (
Grade char(64),
block_ID char(64) PRIMARY KEY NOT NULL,
Density char(64),
BatchNumber char(64) NOT NULL,
BlockDateID Datetime
);
That is my table i want to store the data in. There I do not wish to have duplicates on the id. The problem is, while logging I get duplicates since I log on change. Lets say that the batchid is 1, if it becomes 2 while logging. I will get a blockid twice, both with batch number 1 and 2. How do I pick the latter?
Hope I explained enough for guidance. While logging they look like this:
id SiemensTiaV15_s71200_BatchTester_NewBatchIDValue_VALUE SiemensTiaV15_s71200_BatchTester_TestWriteValue_VALUE SiemensTiaV15_s71200_BatchTester_TestWriteValue_TIMESTAMP SiemensTiaV15_s71200_MainTank_Density_VALUE SiemensTiaV15_s71200_MainTank_Grade_VALUE
1 00545 S0047782 2020-06-09 11:18:44.583 0 xxxxx
2 00545 S0047783 2020-06-09 11:18:45.800 0 xxxxx
Please use below query,
select * from
(select id, SiemensTiaV15_s71200_BatchTester_NewBatchIDValue_VALUE,SiemensTiaV15_s71200_BatchTester_TestWriteValue_VALUE, SiemensTiaV15_s71200_BatchTester_TestWriteValue_TIMESTAMP, SiemensTiaV15_s71200_MainTank_Density_VALUE,SiemensTiaV15_s71200_MainTank_Grade_VALUE,
row_number() over (partition by SiemensTiaV15_s71200_BatchTester_NewBatchIDValue_VALUE order by SiemensTiaV15_s71200_BatchTester_TestWriteValue_TIMESTAMP desc) as rnk
from table_name) qry
where rnk=1;
INTO #temp FROM Block; INSERT INTO Product_log(Grade, block_ID, Density, BatchNumber, BlockDateID)
selct NewBatchIDValue_VALUE, TestWriteValue_VALUE, TestWriteValue_TIMESTAMP,
Density_VALUE, Grade_VALUE from
(select NewBatchIDValue_VALUE, TestWriteValue_VALUE,
TestWriteValue_TIMESTAMP, Density_VALUE, Grade_VALUE, row_number() over
(partition by BatchTester_NewBatchIDValue_VALUE order by
BatchTester_TestWriteValue_VALUE) as rnk from #temp) qry
where rnk = 1;
My question would be better served as a comment on Limit result set in sql window function , but I don't have the necessary reputation to comment.
Given a table of moving vehicle locations, for each vehicle I wish to find the most recent recorded position (and other data about the vehicle at that time). Based on answers in the other question, I can run a query like:
Table definition:
CREATE TABLE VehiclePositions
(
Id BIGINT NOT NULL,
VehicleID NVARCHAR(12) NULL,
Timestamp DATETIME NULL,
PositionX FLOAT NULL,
PositionY FLOAT NULL,
PositionZ SMALLINT NULL,
Speed SMALLINT NULL,
Heading SMALLINT NULL
)
Query:
select *
from
(select
*,
row_number() over (partition by VehicleID order by Timestamp desc) as ranking
from VehiclePositions) as x
where
ranking = 1
Now, the problem is that this does a full table scan. I thought that by creating an appropriate index, I could avoid this:
CREATE INDEX idx_VehicPosition ON VehiclePositions(VehicleID, Timestamp);
However, SQL Server will happily ignore this index in the query and still perform the stable scan.
Note: I can get SQL Server to use the index, but the code is rather ugly:
DECLARE #ids TABLE (id NVARCHAR(12) UNIQUE)
INSERT INTO #ids
SELECT DISTINCT VehicleID
FROM VehiclePositions
SELECT ep.*
FROM VehiclePositions vp
WHERE Timestamp = (SELECT Max(TimeStamp) FROM VehiclePositions vp2
WHERE vp2.VehicleID = vp.VehicleID)
AND VehicleID IN (SELECT DISTINCT id FROM #ids)
(The VehicleID IN... is because it seems SQL Server doesn't implement seek-skip optimisations. It still comes up with a pretty non-optimal query plan that visits the index twice, but at least it doesn't execute in linear time).
Is there a way to make SQL Server run the window function query intelligently?
I'm using SQL Server 2014...
Help will be appreciated
What i would do :
SELECT *
FROM
(SELECT MAX(Timestamp) as maxtime,
VehicleID
FROM VehiclePositions
GROUP BY VehicleID ) as maxed INNER JOIN
(SELECT Id ,
VehicleID ,
Timestamp ,
PositionX ,
PositionY,
PositionZ,
Speed ,
Heading
FROM VehiclePositions) as vals
ON maxed.maxtime = vals.Timestamp
AND maxed.VehicleID = vals.VehicleID
to my knowledge you cant get around your index getting scanned twice.
As long as you are selecting all vehicles from the table and are select all column (or at least columns that are not in your index), I would expect the table scan to keep popping up.
In many cases, that will actually be the most efficient query plan. Only if you have a many rows per vehicle (like several pages) a seek strategy might be faster.
If you do have a lot of rows per vehicle, you might consider partitioning your table on Timestamp...
You can filter results in windows function using 'qualify', as follows:
select *
from VehiclePositions
qualify row_number() over (partition by VehicleID order by Timestamp desc) = 1
Suppose I have a table with even number of rows. For eg- a table Employee with two columns Name and EmpCode. The table looks like
Name EmpCode
Ajay 7
Vikash 5
Shalu 4
Hari 8
Anu 1
Puja 9
Now, I want my output in reverse of EmpCode like:
Name EmpCode
Ajay 9
Vikash 1
Shalu 8
Hari 4
Anu 5
Puja 7
I need to run this query in SQL Server.
As the OP hasn't replied, I'll post a little explanation for them instead. As everyone has eluded to, tables in SQL Server have no built in ordering. Your data is stored in what is known as a HEAP. This means, when you run a query without an ORDER BY your data can return in any order that the Server feels like. With small datasets this might be in the order you inserted it in, but that's just it (it might).
When you get to larger datasets, and when you have multiple cores running on the operation, then the order of a SELECT * FROM [Table]; is more likely to not be the order in insertion, and is more likely to be random which each instance of running the query. I have several tables where a SELECT TOP 1 *... will return a different row every time I run the query; even with the CLUSTERED INDEX.
The only, yes only, way to guarantee the order is by using ORDER BY. Now, you might have another column which you haven't shared that you can order by, but if not, perhaps this (very) simple example will at least assist you, if nothing else:
CREATE TABLE #Employee ([Name] varchar(10), EmpCode tinyint);
INSERT INTO #Employee
VALUES ('Ajay',7),
('Vikash',5),
('Shalu',4),
('Hari',8),
('Anu',1),
('Puja',9);
GO
--Just SELECT *. ORDER is NOT guaranteed, but, due to the low volume of data, will probably be in the order by insertion
SELECT *
FROM #Employee;
--But, we want to reverse the order, so, let's add an ORDER BY
SELECT *
FROM #Employee
ORDER BY [Name];
--Oh! That didn't work (duh). Let's try again
SELECT *
FROM #Employee
ORDER BY Empcode;
--Nope, this isn't working. That's because your data has nothing related to it's insertion order. So, let's give it one:
GO
DROP TABLE #Employee;
CREATE TABLE #Employee (ID int IDENTITY(1,1), --Oooo, what is this?
[Name] varchar(10),
EmpCode tinyint);
INSERT INTO #Employee
VALUES ('Ajay',7),
('Vikash',5),
('Shalu',4),
('Hari',8),
('Anu',1),
('Puja',9);
GO
--Now look
SELECT *
FROM #Employee;
--So, we can use an ORDER BY, and get the correct order too
SELECT [Name],
Empcode
FROM #Employee
ORDER BY ID;
--So, we got the right ORDER using an ORDER BY. Now we can do something about the ordering:
--We'll need a CTE for this:
WITH RNs AS(
SELECT *,
ROW_NUMBER() OVER (ORDER BY ID ASC) AS RN1,
ROW_NUMBER() OVER (ORDER BY ID DESC) AS RN2
FROM #Employee)
SELECT R1.[Name],
R2.EmpCode
FROM RNs R1
JOIN RNs R2 ON R1.RN1 = R2.RN2;
GO
DROP TABLE #Employee;
I have a UI that allows a user to select one or more fields they want to add to a table. This data also has an orderID associated with it that determines the field order.
When the user adds new fields, I need to find the last orderID this user used and increment it by 1, submitting all of the new fields.
For example, if there is a single record that already exists in the database, it would have an orderID of 1. When I choose to add three more fields, it would check to see the last orderID I used (1) and then increment it for each of the new records it adds, 1-4.
-- Get the last ID orderID for this user and increment it by 1 as our starting point
DECLARE #lastID INT = (SELECT TOP 1 orderID FROM dbo.BS_ContentRequests_Tasks_User_Fields WHERE QID = #QID ORDER BY orderID DESC)
SET #lastID = #lastID+1;
-- Create a temp table to hold our fields that we are adding
DECLARE #temp AS TABLE (fieldID int, orderID int)
-- Insert our fields and incremented numbers
INSERT INTO #temp( fieldID, orderID )
SELECT ParamValues.x1.value('selected[1]', 'int'),
#lastID++
FROM #xml.nodes('/root/data/fields/field') AS ParamValues(x1);
Obviously the #lastID++ part is where my issue is but hopefully it helps to understand what I am trying to do.
What other method could be used to handle this?
ROW_NUMBER() ought to do it.
select x.Value,
ROW_NUMBER() over (order by x.Value) + #lastID
from (
select 10 ParamValues.x1.value('selected[1]', 'int') Value
from #xml.nodes('/root/data/fields/field') AS ParamValues(x1)
) x
You could use a column with IDENTITY(1,1)
If you want OrderID to be unique across the entire table then see below:
Click here to take a look at another post that addresses this issue.
There are multiple ways to approach this issue, but in this case, the easiest, while reasonable, means may be to use an identity column. However, that is not as extensible as using a sequence. If you feel that you may need more flexibility in the future, then use a sequence.
If you want OrderID to be unique across the fields inserted in one batch then see below:
You should take a closer look at Chris Steele's answer.
I have a table, Core_Faculty with 4 fields: ID (PK - INT), InstitutionID (INT), PersonID (INT), DeprecatedDate (SMALLDATETIME)
What I'd like to do is delete all the records for institution/person combinations that have both deprecated records and non-deprecated (DeprecatedDate IS NULL) record, but keep the non-deprecated record.
If an institution/person combination has only just one record (whether deprecated or not), I'd like to keep those and leave them alone. I'm only considering records that have both DeprecatedDate IS NULL and Deprecated IS NOT NULL for each unique institution/person combination.
End goal is to be left with one record per institution/person combination whether deprecated or not, but giving priority to the record that has a NULL deprecated date. These are the good, live records. However, if we are starting with only one record and it's deprecated, go ahead and keep it.
The database currently only can potentially have one of each as institution/person/deprecateddate is a unique key on the table.
How would I go about solving this, and what methods can I use to find the appropriate records, while only considering records that have both deprecated and non-deprecated values for the combination?
DELETE f
FROM
Core_Faculty f
INNER JOIN
(
SELECT *,
ROW_NUMBER() OVER (
PARTITION BY
f.InstitutionID,
f.PersonID
ORDER BY
CASE
WHEN f.DeprecatedDate IS NULL THEN 1
ELSE 2
END,
f.DeprecatedDate
) RowNum
FROM
Core_Faculty f
) d ON
f.ID = d.ID
WHERE
d.RowNum > 1;
In SQL Server you can use a common table expression with a ROW_NUMBER function to identify the rows you want to keep:
WITH cte AS (
SELECT [ID]
,[InstitutionID]
,[PersonID]
,[DeprecatedDate]
,ROW_NUMBER() OVER (PARTITION BY [InstitutionID], [PersonID]
ORDER BY [DeprecatedDate] DESC) as [RowNumber]
FROM [Blog].[dbo].[Core_Faculty]
)
SELECT [ID]
,[InstitutionID]
,[PersonID]
,[DeprecatedDate]
,[RowNumber]
FROM cte
--WHERE [RowNumber] = 1
The ORDER BY [DeprecatedDate] DESC part will make ensure the latest record is the 1st row in the [InstitutionID], [PersonID] grouping. If there is only one row, even if it is a null, it will be kept since it is the 1st row in the grouping.
You can then use
DELETE
FROM cte
WHERE [RowNumber] > 1
instead of the select to remove the rest of the rows. Leaving you with just one row person/institution combo.