I need confirmation for one "tricky" question.
I am in a transaction, in which i insert some rows in a table.
After that, querying the same table, and based on the results, i insert in another table.
My question is: Will the inserted rows in the first table be visible when inserting in the second table? (I need the inserted rows to be visible).
My first Insert Is :
INSERT INTO BioUsers Select NewId(),A.BadgeNr,GetDate(),A.PersNr
FROM (
SELECT CB.Persnr,C.BadgeNr FROM CurBioDistribution CB
INNER JOIN CUR C ON C.PersNr = CB.PersNr
WHERE
CB.[Type] = 1
AND CB.GroupNr = #Nr
AND CB.PersNr IN (SELECT PersNr FROM CurBioDistribution WHERE GroupNr = #Nr)
EXCEPT (SELECT PersNr, BadgeId as BadgeNr FROM BioUsers)
) A
I want To insert all the BioUserID's in the first table in another table, which contains the field BioUserID, but only if they are not already in it. So when select from the first one, i want to get the inserted rows too.
PS: I searched for this problem, but i could only find answers about this issue when multiple transaction (from different clients) are involved.
If both inserts are in the same transaction, then yes.
If not then you are in what you described as a multi-user scenario. Multi user is infact misleading, multi transaction would be more correct.
Related
I have an INSERT trigger of a table, where one field of the table contains a comma-separated list of key-value pairs, that are separated by a :
I can select this field with the two values into a temp table easily with this statement:
-- SAMPLE DATA FOR PRESENTATION ONLY
DECLARE #messageIds VARCHAR(2000) = '29708332:55197,29708329:54683,29708331:54589,29708330:54586,29708327:54543,29708328:54539,29708333:54538,29708334:62162,29708335:56798';
SELECT
SUBSTRING(value, 1,CHARINDEX(':', value) - 1)AS MessageId,
SUBSTRING(value, CHARINDEX(':', value) + 1, LEN(value)-SUBSTRING(value,0,CHARINDEX(value,':'))) AS DeviceId
INTO #temp_messages
FROM STRING_SPLIT(#messageIds, ',')
SELECT * FROM #temp_messages
DROP TABLE #temp_messages
The result will look like this
29708332 55197
29708329 54683
29708331 54589
29708330 54586
29708327 54543
29708328 54539
29708333 54538
29708334 62162
29708335 56798
From here I can join the temp table to other tables and insert some of the results into a third table.
Inside the trigger I can get the messageIds with a simple SELECT statement like
DECLARE #messageIds VARCHAR(2000) = (SELECT ProcessMessageIds FROM INSERTED)
Now I create the temp table (like described above) and process my
INSERT INto <new_table> SELECT col1, col1, .. FROM #temp_messages
JOIN <another_table> ON ...
Unfortunately this will only work for single row inserts. As soon as there is more than one row, my SELECT ProcessMessageIds FROM INSERTED will fail, as there are multiple rows in the INSERTED table.
I can process the rows in a CURSOR but as far as I know CURSORS are a no-go in triggers and I should avoid them whenever it is possible.
Therefore my question is, if there is another way to do this without using a CURSOR inside the trigger?
Before we get into the details of the solution, let me point out that you would have no such issues if you normalized your database, as #Larnu pointed out in the comment section of your question.
Your
DECLARE #messageIds VARCHAR(2000) = (SELECT ProcessMessageIds FROM INSERTED)
statement assumes that there will be a single value to be assigned to #messageIDs and, as you have pointed out, this is not necessarily true.
Solution 1: Join with INSERTED rather than load it into a variable
INSERT INTO t1
SELECT ...
FROM t2
JOIN T3
ON ...
JOIN INSERTED
ON ...
and then you can reach INSERTED.ProcessMessageIds without issues. This will no longer assume that a single value was used.
Solution 2: cursors
You can use a CURSOR, as you have already pointed out, but it's not a very good idea to use cursors inside a trigger, see https://social.msdn.microsoft.com/Forums/en-US/87fd1205-4e27-413d-b040-047078b07756/cursor-usages-in-trigger-in-sql-server?forum=aspsqlserver
Solution 3: insert a single line at a time
While this would not require a change in your trigger, it would require a change in how you insert and it would increase the number of db requests necessary, so I would advise you not to choose this approach.
Solution 4: normalize
See https://www.simplilearn.com/tutorials/sql-tutorial/what-is-normalization-in-sql
If you had a proper table rather than a table of composite values, you would have no such issues and you would have a much easier time to process the message ids in general.
Summary
It would be wise to normalize your tables and perform the refactoring that would be needed afterwards. It's a great effort now, but you will enjoy its fruits. If that's not an option, you can "act as if it was normalized" and choose Solution 1.
As pointed out in the answers, joining with the INSERTED table solved my problem.
SELECT INTAB.Id,
SUBSTRING(value, 1,CHARINDEX(':', value) - 1)AS MessageId,
SUBSTRING(value, CHARINDEX(':', value) + 1, LEN(value)-SUBSTRING(value,0,CHARINDEX(value,':'))) AS DeviceId
FROM INSERTED AS INTAB
CROSS APPLY STRING_SPLIT(ProcessMessageids,',')
I never used "CROSS APPLY" before, thank you.
I have two tables:
Order and
Product.
I want a specific column(OnShelfQuantity) in the Product table to be updated as a new row is added in the Order table. I have used the below query to implement a trigger which will do that. But the problem is that when I insert a row in the Order table and then later check the Product table to see the changes, I notice that the Product table has been updated 3 times. For e.g: Order quantity inserted = 10, then only 10 should be subtracted from Product_TAB.OnShelfQuantity. But 30 gets subtracted. Please help!
create trigger dbo.Trigge
ON dbo.Ordertable
AFTER INSERT
AS
BEGIN
update Product_TAB set OnShelfQuantity= Product_TAB.OnShelfQuantity - Ordertable.Quantity
FROM dbo.Product_TAB
INNER JOIN Ordertable
ON Ordertable.ProductID = Product_TAB.ProductID;
END;
I think, you can use INSERTED table to resolve this Issue.
Inserted table is a table which is used by triggers to store the frequently inserted records in the tables.
So, you can use the same in your update statement to avoid this.
update Product_TAB set OnShelfQuantity= Product_TAB.OnShelfQuantity -
Ordertable.Quantity
FROM dbo.Product_TAB
INNER JOIN Ordertable ON Ordertable.ProductID = Product_TAB.ProductID
INNER JOIN inserted INS ON INS.Order_ID=Ordertable.Order_ID
You can have multiple rows in the inserted table. And, these rows could have the same product. A row in the target table is only updated once in an update statement. Hence, you want to aggregate the data before the update:
create trigger dbo.Trigge
ON dbo.Ordertable
AFTER INSERT
AS
BEGIN
update p
set OnShelfQuantity= p.OnShelfQuantity - i.total_quantity
from dbo.Product_TAB p JOIN
(SELECT i.ProductId, SUM(i.Quantity) as total_quantity
FROM inserted i
GROUP BY i.ProductId
) i
on i.ProductID = p.ProductID;
END;
Note that this only uses inserted and not the original table.
So the issue was that I was inserting new rows but with the same Order ID. This is why it was doing additional subtraction which I didn't require. So now I have to just insert a new row but with unique OrderID. Thanks to everyone who replied above!
I was reviewing creating DML triggers in SQL Server in SQL docs: Use the inserted and deleted Tables
There is an example which do the following:
The following example creates a DML trigger. This trigger checks to make sure the credit rating for the vendor is good when an attempt is made to insert a new purchase order into the PurchaseOrderHeader table. To obtain the credit rating of the vendor corresponding to the purchase order that was just inserted, the Vendor table must be referenced and joined with the inserted table. If the credit rating is too low, a message is displayed and the insertion does not execute.
Note that this example does not allow for multirow data modifications.
USE AdventureWorks2012;
GO
IF OBJECT_ID ('Purchasing.LowCredit','TR') IS NOT NULL
DROP TRIGGER Purchasing.LowCredit;
GO
-- This trigger prevents a row from being inserted in the Purchasing.PurchaseOrderHeader table
-- when the credit rating of the specified vendor is set to 5 (below average).
CREATE TRIGGER Purchasing.LowCredit
ON Purchasing.PurchaseOrderHeader
AFTER INSERT
AS
IF EXISTS (SELECT *
FROM Purchasing.PurchaseOrderHeader p
JOIN inserted AS i ON p.PurchaseOrderID = i.PurchaseOrderID
JOIN Purchasing.Vendor AS v ON v.BusinessEntityID = p.VendorID
WHERE v.CreditRating = 5)
BEGIN
RAISERROR ('A vendor''s credit rating is too low to accept new purchase orders.', 16, 1);
ROLLBACK TRANSACTION;
RETURN
END;
GO
I wonder why the example inner joined the inserted table with Purchasing.PurchaseOrderHeader table and then join the vendor table.
Can I get the same result using only the inserted table joining the vendor table directly without joining with Purchasing.PurchaseOrderHeader table?
Not only do I believe you are correct, I think there are further inaccuracies on this documentation page - which I have to admit is pretty rare in my experience.
Take for example this part:
Note that this example does not allow for multirow data modifications.
This is a false claim. The trigger code example will handle multiple rows insert as well as a single row insert.
Note that according to the documented (and observed) behavior, the inserted table will contain all the rows inserted (or updated) to the trigger's target table:
The inserted table stores copies of the affected rows during INSERT and UPDATE statements. During an insert or update transaction, new rows are added to both the inserted table and the trigger table. The rows in the inserted table are copies of the new rows in the trigger table.
Therefor, the join to inserted should be enough in this case to enforce the business rule discussed.
That being said, using triggers to enforce business rules might prove difficult and even problematic - note that this trigger only covers inserted rows, but not updated rows. This means that a new row might be inserted with valid values, and later on updated to invalid values.
I have a number of queries that are run at the same time but now I want the result to populate a permanent table that I've created.
Each of the queries will have a column called 'Descript' which is what I want all the results to join to so i want to make sure that if the Descript column is out of order (or null) on one of the queries it will link the figures to the correct Descript.
I performed an INTO after the end of each query being run but this didn't work.
The first level of data went in but the second level just went underneath the first (if that makes sense) creating more rows.
INSERT INTO dbo.RESULTTABLE (Descript, Category, DescriptCount)
SELECT Descript, Category, DescriptCount
FROM #Query1
I have around 15 queries to join into 1 table so any help to understand the logic is appreciated.
Thanks
If I understood your question clearly, you want to insert query results which is not stored in the Temptable and update already existing records in the table.
update R set Category = Q.Category, DescriptCount = Q.DescriptCount,
from #ResultTable R inner join #Query1 Q ON R.Descript = Q.Descript
INSERT INTO dbo.RESULTTABLE (Descript, Category, DescriptCount)
SELECT Descript, Category, DescriptCount FROM #Query1 where Descript NOT IN (select Descript from #ResultTable)
Then you can process the same approach for other queries.
I have a problem where I need to check that two columns in each table in a database are unique.
We have the database with barcode entries called uid and rid.
Table 1: T1.uid
And
Table 2: T2.rid
No barcodes in the two table columns must be the same.
How can we ensure that.
If a insertion of a barcode into table T1.uid matches an entry in
T2.rid we want to throw an error.
The tables are cleaned up and is in a consistent state where the entries in
T1.uid and T2.rid are unique over both table columns.
It is not possible to insert NULL values in the tables respective uid and tid column(T1.uid and T2.rid)
It is not possible to create a new table for all barcodes.
Because we don't have full control of the database server.
EDIT 19-02-2015
This solution cannot work for us, because we cannot make a new table
to keep track of the unique names(see table illustration).
We want to have a constraint over two columns in different tables without changing the schema.
Per the illustration we want to make it impossible for john to exist in
T2 because he already exists in table T1. So an error must be "thrown"
when we try to insert John in T2.Name.
The reason is that we have different suppliers that inserts into these tables
in different ways, if we change the schema layout, all suppliers would
need to change their database queries. The total work is just to much,
if we force every suppplier to make changes.
So we need something unobtrusive, that doesnt require the suppliers to change
their code.
A example could be that T1.Name is unique and do not accept NULL values.
If we try insert an existing name, like "Alan", then an exception will occur
because the column has unique values.
But we want to check for uniqueness in T2.Name at the same time.
The new inserted value should be unique over the two tables.
Maybe something like this:
SELECT uid FROM Table1
Where Exists (
SELECT rid FROM Table2
WHERE Table1.uid = rid )
This will show all rows from Table1 where their column uid has an equivalent in column rid of Table2.
The condition before the insertion happens could look like below. #Idis the id you need to insert the data for.
DECLARE #allowed INT;
SELECT #allowed = COUNT(*)
FROM
(
SELECT T1.uid FROM T1 WHERE T1.uid = #Id
UNION ALL
SELECT T2.rid FROM T2 WHERE T2.rid = #id
)
WHERE
#id IS NOT NULL;
IF #allowed = 0
BEGIN
---- insert allowed
SELECT 0;
END
Thanks to all who answered.
I have solved the problem. A trigger is added to the database
everytime an insert or update procedure is executed, we catch it
check that the value(s) to be inserted doens't exist in the columns of the two
tables. if that check is succesfull we exceute the original query.
Otherwise we rollback the query.
http://www.codeproject.com/Articles/25600/Triggers-SQL-Server
Instead Of Triggers