I am having problems getting a SQL trigger to do what I want. I need to populate a field in a table when another field is updated. More specifically, when an employee ID is entered I need to generate Unicode to make a barcode work. I have written code to generate the unicode, I just need the trigger to function.
This is the skeleton of what I need:
CREATE TRIGGER Unicode
AFTER UPDATE of unique.id
ON table [dbo].table
FOR EACH ROW???
AS
BEGIN
SELECT (unique.id2
now I need to set unique.id2 to the unicode function that I wrote
I feel like I am on the wrong track with this.
Here is an image of the database I am working with (I did not create it) http://i.imgur.com/4wkfY.png. Running SQL server 2008
When PersonalDataID[2] is updated (employee ID). I need to generate code for PersonalDataID[32].
Thank you for any help you can give!
To become proficient in SQL Server, the first thing you need to do is become comfortable with the fact that most operations work best when applied as a set. Thinking in terms of "for each row" will almost always lead you down the wrong path.
In this case, since an update can affect multiple rows, you need to deal with all of those rows at once. You can do this by using the inserted pseudo-table. I looked at your picture but your sample code is quite a mess and I have no idea how to correlate the two. So here is a quick example that you will have to tailor to your actual schema.
CREATE TRIGGER dbo.UpdateUnicodeColumn
ON dbo.table
FOR UPDATE
AS
BEGIN
SET NOCOUNT ON;
UPDATE t SET BarcodeColumn = (your calculation, a function, maybe?)
FROM dbo.table AS t
INNER JOIN inserted AS i
ON t.key = i.key;
END
GO
Here's the syntax. Just replace somefield with whatever field you need entered and DestinationTable with the table you want to add the Unicode record to.
CREATE TRIGGER Unicode ON SomeTable
AFTER UPDATE
AS
INSERT INTO DestinationTable
(somefield)
SELECT somefield FROM INSERTED
GO
I don't think you need 'FOR EACH ROW???' :P
CREATE TRIGGER Unicode
ON table [dbo].table
AFTER UPDATE of unique.id
AS
Begin
(SELECT unique.id2...)
Overall reference the answer above.
Related
I'm writing a trigger in which I need to check the incoming data and potentially change it. Then later in the trigger I need to use that new data for further processing. A highly simplified version looks something like this:
ALTER TRIGGER [db].[trig_update]
ON [db].[table]
AFTER UPDATE
AS
BEGIN
DECLARE #thisprofileID int
IF (Inserted.profileID IS NULL)
BEGIN
SELECT #thisprofileID=profileID
FROM db.otherTable
WHERE userid = #thisuserID;
UPDATE db.table
SET profileID = #thisprofileID
WHERE userid = #thisuserID;
-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
END
IF ({conditional})
BEGIN
UPDATE db.thirdTable
SET [profileID] = Inserted.profileID
...{20+ other fields}
FROM Inserted ...{a few joins}
WHERE {various criteria}
END
END
The problem that we're running into is that the update statement fails because Inserted.profileID is null, and thirdTable.profileID is set to not allow nulls. table.profileID will never stay null; if it is created as null then this trigger should catch it and set it to a value. But even though we're updated 'table', Inserted still has the null value. So far it makes sense to me why this is happening.
I'm unsure how to correct the problem. In the area with commented Xs I tried running an update query against the Inserted table to update profileID, but this resulted in an error because the pseudo-table apparently can't be updated. Am I incorrect in this presumption? That would be an easy solution.
The next most logical solution to me would be to INSERT INTO a table variable to make a copy of Inserted and then use that in the rest of the trigger, but that fails because the table variable is not defined. Defining that table variable would require more fields than I care to count, and will present a major maintenance nightmare any time that we need to make changes to the structure of 'table'. So assuming this is the best approach, is there an easy way to copy the data and structure of Inserted into a table variable without explicitly defining the structure?
I don't think that a temp table (which I could otherwise easily insert into) would be a good solution because my limited understanding is that they are far slower than a table variable that lives only inside the trigger. I assume that temp table also must be public, and cause problems if our trigger fires twice and both instances need the temp table.
I'd like to find out how to update a temporary table before I show the query. This is to avoid making permanent changes to the database.
So far I got the following:
WITH
new_salary AS
(SELECT ID,NAME,DEPT_NAME,SALARY FROM INSTRUCTOR WHERE DEPT_NAME='Comp. Sci.')
SELECT
*
FROM
new_salary
WHERE
DEPT_NAME='Comp. Sci.';
Now here is where it ends. I want to update this temporary table and show the updated version of that table as to avoid changing the actual database. All my attempts at using the UPDATE clause have failed so I am kind of dumbfounded :/
This part I am currently trying to do is not part of homework. It's just me who doesn't want to have to re-do the database over and over.
How would I go about doing this?
I guess you have two options:
You make a procedure, which first checks whether it needs to update the table. After calling that you execute the query.
You create a pipelined function, which does the checking and returning of the data. You could integrate this into the select like this (pipelined function name called pipelined_function_name):
select *
from table(pipelined_function_name)
;
How do I debug a complex query with multiple nested sub-queries in SQL Server 2005?
I'm debugging a stored procedure and trigger in Visual Studio 2005. I'd like to be able to see what the results of these sub-queries are, as I feel that this is where the bug is coming from. An example query (slightly redacted) is below:
UPDATE
foo
SET
DateUpdated = ( SELECT TOP 1 inserted.DateUpdated FROM inserted )
...
FROM
tblEP ep
JOIN tblED ed ON ep.EnrollmentID = ed.EnrollmentID
WHERE
ProgramPhaseID = ( SELECT ...)
Visual Studio doesn't seem to offer a way for me to Watch the result of the sub query. Also, if I use a temporary table to store the results (temporary tables are used elsewhere also) I can't view the values stored in that table.
Is there anyway that I can add a watch or in some other way view these sub-queries? I would love it if there was some way to "Step Into" the query itself, but I imagine that wouldn't be possible.
Ok first I would be leary of using subqueries in a trigger. Triggers should be as fast as possible, so get rid of any correlated subqueries which might run row by row instead of in a set-based fashion. Rewrite to joins. If you only want to update records based on what was in the inserted table, then join to it. Also join to the table you are updating. Exactly what are you trying to accomplish with this trigger? It might be easier to give advice if we understood the business rule you are trying to implement.
To debug a trigger this is what I do.
I write a script to:
Do the actual insert to the table
without the trigger on on it
Create a temp table named #inserted
(and/or one named #deleted)
Populate the table as I would expect
the inserted table in the trigger to
be populated from the insert you do.
Add the trigger code (minus the
create or alter trigger parts)
substituting #inserted every time I
reference inserted. (if you plan to
run multiple times until you are
ready to use it in a trigger throw
it in an explicit transaction and
rollback after checking your
results.
Add a query to check the table(s)
you are changing with the trigger for
the values you wanted to change.
Now if you need to add debug
statements to see what is happening
between steps, you can do so.
Run making changes until you get the
results you want.
Once you have the query working as
you expect it to, it is easy to take
the # signs off inserted and use it
to create the body of the trigger.
This is what I usually do in this type of scenerio:
Print out the exact sqls getting generated by each subquery
Then run each of then in the Management Studio as suggested above.
You should check if different parts are giving you the right data you expect.
If you create a new trigger in MS SQL Management Studio by using the GUI, it gives you this template:
--====================================
-- Create database trigger template
--====================================
USE <database_name, sysname, AdventureWorks>
GO
IF EXISTS(
SELECT *
FROM sys.triggers
WHERE name = N'<trigger_name, sysname, table_alter_drop_safety>'
AND parent_class_desc = N'DATABASE'
)
DROP TRIGGER <trigger_name, sysname, table_alter_drop_safety> ON DATABASE
GO
CREATE TRIGGER <trigger_name, sysname, table_alter_drop_safety> ON DATABASE
FOR <data_definition_statements, , DROP_TABLE, ALTER_TABLE>
AS
IF IS_MEMBER ('db_owner') = 0
BEGIN
PRINT 'You must ask your DBA to drop or alter tables!'
ROLLBACK TRANSACTION
END
GO
Should I use this template?
I dont know anything about triggers, but I think I need to use them. The purpose in this case is that on an insert to the table, I need to update one of the fields.
Please help me get started!
OK to begin with that is the wrong template if you want an ordinary trigger that one is a trigger on making structural changes to the table itself.
If you decide to do a trigger that affects data (as opposed to structure), there are several things you need to know. First and by far the most critical, triggers operate on sets of data not one row at time. You must write any trigger to handle multiple row inserts.updates or deletes. If you end up with any code setting the value in inserted or deleted to a variable, there is a 99% chance it will not work properly if multiple records are involved.
What is inserted or deleted you ask? That is the next thing you need to know about triggers, there are two pseudotables (inserted and deleted) that are only available in a trigger (or an output clause) which contain the new information being inserted or the updated values (in the inserted table) and the old information being deleted or being changed by an update (in the deleted table). So an insert has values in inserted, a delete has values in deleted and an update has values in both. Use these in your trigger to pull the values you need to change.
Since you don't know anything about triggers, I would say no, don't use the template.
Read the books online page for Create Trigger and write the trigger by hand.
There is probably more in that template code than you actually need. Read the manual and keep it simple.
If you don't know anything about triggers then I would strongly suggest that you read up on them before implementing them. Get Triggers right and they can make your life a lot easier; get it wrong and Triggers will cause you a lot of trouble.
I would suggest starting off with this tutorial
http://www.sqlteam.com/article/an-introduction-to-triggers-part-i
You can use the above SQL as a template or you can simply write your own. I would suggest you write your own as you'll understand what you are doing. Obviously only do this after you have done some serious reading on triggers. Check out MSDN too
Is it possible to force a column in a SQL Server 2005 table to a certain value regardless of the value used in an insert or update statement is? Basically, there is a bug in an application that I don't have access to that is trying to insert a date of 1/1/0001 into a datetime column. This is producing a SqlDateTime overflow exception. Since this column isn't even used for anything, I'd like to somehow update the constraints on the columns or something in the database to avoid the error. This is obviously just a temporary emergency patch to avoid the problem... Ideas welcome...
How is the value being inserted? If it's through a stored proc... you could just modify the Sproc to ignore that input parameter.
if it's through client-side generated SQL, or an ORM tool, otoh, then afaik, the only option is a "Before" Trigger that "replaces" the value with an acceptable one...
If you're using SQL 2005 you can create an INSTEAD OF trigger.
The code in this trigger wil run in stead of the original insert/update
-Edoode
I'd create a trigger to check and change the value
If it is a third party application then I will assume you don't have access to the Stored Procedure, or logic used to generate and insert that value (it is still worth checking the SPs for the application's database though, to see if you can modify them).
As Charles suggested, if you don't have access to the source, then you need to have a trigger on the insert.
The Microsoft article here will give you some in depth information on creating triggers.
However, SQL Server doesn't have a true 'before insert' trigger (to my knowledge), so you need to try INSTEAD OF. Have a look here for more information. In that article, pay particular note of section 37.7, and the following example (again from that article):
CREATE TRIGGER T_InsertInventory ON CurrentInventory
INSTEAD OF INSERT AS
BEGIN
INSERT INTO Inventory (PartNumber, Description, QtyOnOrder, QtyInStock)
SELECT PartNumber, Description, QtyOnOrder, QtyInStock
FROM inserted
END
Nick.
the simplest hack would be to make it a varchar, and let it insert that as a string into the column.
The more complicated answer is, you can massage the data with a trigger, but it would still have to be valid in the first place. For instance I can reset a fields value in an update/insert trigger, but it would still have to get through the insert first.