I have something like the table below:
CREATE TABLE updates (
id INT PRIMARY KEY IDENTITY (1, 1),
name VARCHAR (50) NOT NULL,
updated DATETIME
);
And I'm updating it like so:
INSERT INTO updates (name, updated)
VALUES
('fred', '2020-11-11),
('fred', '2020-11-11'),
...
('bert', '2020-11-11');
I need to write an after update Trigger and enumerate all the name(s) that were added and add each one to another table but can't work out how enumerate each one.
EDIT: - thanks to those who pointed me in the right direction, I know very little SQL.
What I need to do is something like this
foreach name in inserted
look it up in another table and
retrieve a count of the updates a 'name' has done
add 1 to the count
and update it back into the other table
I can't get to my laptop at the moment, but presumably I can do something like:
BEGIN
SET #count = (SELECT UCount from OTHERTAB WHERE name = ins.name)
SET #count = #count + 1
UPDATE OTHERTAB SET UCount = #count WHERE name = ins.name
SELECT ins.name
FROM inserted ins;
END
and that would work for each name in the update?
Obviously I'll have to read up on set based SQL processing.
Thanks all for the help and pointers.
Based on your edits you would do something like the following... set based is a mindset, so you don't need to compute the count in advance (in fact you can't). It's not clear whether you are counting in the same table or another table - but I'm sure you can work it out.
Points:
Use the Inserted table to determine what rows to update
Use a sub-query to calculate the new value if its a second table, taking into account the possibility of null
If you are really using the same table, then this should work
BEGIN
UPDATE OTHERTAB SET
UCount = COALESCE(UCount,0) + 1
WHERE [name] in (
SELECT I.[name]
FROM Inserted I
);
END;
If however you are using a second table then this should work:
BEGIN
UPDATE OTHERTAB SET
UCount = COALESCE((SELECT UCount+1 from OTHERTAB T2 WHERE T2.[name] = OTHERTAB.[name]),0)
WHERE [name] in (
SELECT I.[name]
FROM Inserted I
);
END;
Using inserted and set-based approach(no need for loop):
CREATE TRIGGER trg
ON updates
AFTER INSERT
AS
BEGIN
INSERT INTO tab2(name)
SELECT name
FROM inserted;
END
Related
An example to the problem:
There are 3 columns present in my SQL database.
+-------------+------------------+-------------------+
| id(integer) | age(varchar(20)) | name(varchar(20)) |
+-------------+------------------+-------------------+
There are a 100 rows of different ids, ages and names. However, since many people update the database, age and name constantly change.
However, there are some boundaries to age and name:
Age has to be an integer and has to be greater than 0.
Name has to be alphabets and not numbers.
The problem is a script to check if the change of values is within the boundaries. For example, if age = -1 or Name = 1 , these values are out of the boundaries.
Right now, there is a script that does insert * into newtable where age < 0 and isnumeric(age) = 0 or isnumeric(name) = 0;
The compiled new table has rows of data that have values that are out of the boundary.
I was wondering if there is a more efficient method to do such checking in SQL. Also, i'm using microsoft sql server, so i was wondering if it is more efficient to use other languages such as C# or python to solve this issue.
You can apply check constraint. Replace 'myTable' with your table name. 'AgeCheck' and 'NameCheck' are names of the constraints. And AGE is the name of your AGE column.
ALTER TABLE myTable
ADD CONSTRAINT AgeCheck CHECK(AGE > 0 )
ALTER TABLE myTable
ADD CONSTRAINT NameCheck CHECK ([Name] NOT LIKE '%[^A-Z]%')
See more on Create Check Constraints
If you want to automatically insert the invalid data into a new table, you can create AFTER INSERT Trigger. I have given snippet for your reference. You can expand the same with additional logic for name check.
Generally, triggers are discouraged, as they make the transaction lengthier. If you want to avoid the trigger, you can have a sql agent job to do auditing on regular basis.
CREATE TRIGGER AfterINSERTTrigger on [Employee]
FOR INSERT
AS
BEGIN
DECLARE #Age TINYINT, #Id INT, Name VARCHAR(20);
SELECT #Id = ins.Id FROM INSERTED ins;
SELECT #Age = ins.Age FROM INSERTED ins;
SELECT #Name = ins.Name FROM INSERTED ins;
IF (#Age = 0)
BEGIN
INSERT INTO [EmployeeAudit](
[ID]
,[Name]
,[Age])
VALUES (#ID,
#Name,
#Age);
END
END
GO
all id columns has auto_increment
In my trigger:
ALTER trigger [dbo].[mytrig]
on [dbo].[requests]
after INSERT, UPDATE
as
begin
declare #MyId1 int
set #MyId1 = (select Id from inserted)
declare #MyId2 int
declare #MyId3 int
if (select column1 from inserted) = 1
begin
insert into [dbo].[contracts] select column1,column2,column3 .... from inserted
set #MyId2 = SCOPE_IDENTITY()
insert into [dbo].[History] select column1,column2,column3 .... from inserted
set #MyId3 = SCOPE_IDENTITY()
insert into [dbo].[contracts_depts](Id_Contract ,column5) select #MyId2,column6 from request_depts where Id_request=#MyId1
insert into [dbo].[History_depts] (Id_InHistory,column5) select #MyId3,column6 from request_depts where Id_request=#MyId1
end
end
#MyId1 returns value only after update but not after insert. Do I have to use scope_identity() or something ?
Your main issue is: you're assuming the triggers is called once per row - that is NOT the case!
The trigger is called once per statement, and if your statement affects multiple rows, the Inserted pseudo table will contain multiple rows - so your statement here
set #MyId1 = (select Id from inserted)
really isn't going to work - it will select one arbitrary row (out of however many there are).
You'll need to rewrite your trigger to take this fact into account! Assume that Inserted contains 100 rows - how do you want to deal with that? What are you trying to achieve? Triggers don't return values - they will record into an audit table, or update other rows, or something like that ....
I have a table called Employee. The EmpId column serves as the primary key. In my scenario, I cannot make it AutoNumber.
What would be the best way of generating the the next EmpId for the new row that I want to insert in the table?
I am using SQL Server 2008 with C#.
Here is the code that i am currently getting, but to enter Id's in key value pair tables or link tables (m*n relations)
Create PROCEDURE [dbo].[mSP_GetNEXTID]
#NEXTID int out,
#TABLENAME varchar(100),
#UPDATE CHAR(1) = NULL
AS
BEGIN
DECLARE #QUERY VARCHAR(500)
BEGIN
IF EXISTS (SELECT LASTID FROM LASTIDS WHERE TABLENAME = #TABLENAME and active=1)
BEGIN
SELECT #NEXTID = LASTID FROM LASTIDS WHERE TABLENAME = #TABLENAME and active=1
IF(#UPDATE IS NULL OR #UPDATE = '')
BEGIN
UPDATE LASTIDS
SET LASTID = LASTID + 1
WHERE TABLENAME = #TABLENAME
and active=1
END
END
ELSE
BEGIN
SET #NEXTID = 1
INSERT INTO LASTIDS(LASTID,TABLENAME, ACTIVE)
VALUES(#NEXTID+1,#TABLENAME, 1)
END
END
END
Using MAX(id) + 1 is a bad idea both performance and concurrency wise.
Instead you should resort to sequences which were design specifically for this kind of problem.
CREATE SEQUENCE EmpIdSeq AS bigint
START WITH 1
INCREMENT BY 1;
And to generate the next id use:
SELECT NEXT VALUE FOR EmpIdSeq;
You can use the generated value in a insert statement:
INSERT Emp (EmpId, X, Y)
VALUES (NEXT VALUE FOR EmpIdSeq, 'x', 'y');
And even use it as default for your column:
CREATE TABLE Emp
(
EmpId bigint PRIMARY KEY CLUSTERED
DEFAULT (NEXT VALUE FOR EmpIdSeq),
X nvarchar(255) NULL,
Y nvarchar(255) NULL
);
Update: The above solution is only applicable to SQL Server 2012+. For older versions you can simulate the sequence behavior using dummy tables with identity fields:
CREATE TABLE EmpIdSeq (
SeqID bigint IDENTITY PRIMARY KEY CLUSTERED
);
And procedures that emulates NEXT VALUE:
CREATE PROCEDURE GetNewSeqVal_Emp
#NewSeqVal bigint OUTPUT
AS
BEGIN
SET NOCOUNT ON
INSERT EmpIdSeq DEFAULT VALUES
SET #NewSeqVal = scope_identity()
DELETE FROM EmpIdSeq WITH (READPAST)
END;
Usage exemple:
DECLARE #NewSeqVal bigint
EXEC GetNewSeqVal_Emp #NewSeqVal OUTPUT
The performance overhead of deleting the last inserted element will be minimal; still, as pointed out by the original author, you can optionally remove the delete statement and schedule a maintenance job to delete the table contents off-hour (trading space for performance).
Adapted from SQL Server Customer Advisory Team Blog.
Working SQL Fiddle
The above
select max(empid) + 1 from employee
is the way to get the next number, but if there are multiple user inserting into the database, then context switching might cause two users to get the same value for empid and then add 1 to each and then end up with repeat ids. If you do have multiple users, you may have to lock the table while inserting. This is not the best practice and that is why the auto increment exists for database tables.
I hope this works for you. Considering that your ID field is an integer
INSERT INTO Table WITH (TABLOCK)
(SELECT CASE WHEN MAX(ID) IS NULL
THEN 1 ELSE MAX(ID)+1 END FROM Table), VALUE_1, VALUE_2....
Try following query
INSERT INTO Table VALUES
((SELECT isnull(MAX(ID),0)+1 FROM Table), VALUE_1, VALUE_2....)
you have to check isnull in on max values otherwise it will return null in final result when table contain no rows .
Typically when you specify an identity column you get a convenient interface in SQL Server for asking for particular row.
SELECT * FROM $IDENTITY = #pID
You don't really need to concern yourself with the name if the identity column because there can only be one.
But what if I have a table which mostly consists of temporary data. Lots of inserts and lots of deletes. Is there a simple way for me to reuse the identity values.
Preferably I would want to be able to write a function that would return say NEXT_SMALLEST($IDENTITY) as next identity value and do so in a fail-safe manner.
Basically find the smallest value that's not in use. That's not entirely trivial to do, but what I want is to be able to tell SQL Server that this is my function that will generate the identity values. But what I know is that no such function exists...
I want to...
Implement global data base IDs, I need to provide a default value that I'm in control of.
My idea was based around that I should be able to have a table with all known IDs and then every row ID from some other table that needed a global ID would reference that table. The default value would be provided by something like
INSERT INTO GlobalID
RETURN SCOPE_IDENTITY()
No; it's not unique if it can be reused.
Why do you want to re-use them? Why do you concern yourself with this field? If you want to be in control of it, don't make it an identity; create your own scheme and use that.
Don't reuse identities, you'll just shoot your self in the foot. Use a large enough value so that it never rolls over (64 bit big int).
To find missing gaps in a sequence of numbers join the table against itself with a +/- 1 difference:
SELECT a.id
FROM table AS a
LEFT OUTER JOIN table AS b ON a.id = b.id+1
WHERE b.id IS NULL;
This query will find the numbers in the id sequence for which id-1 is not in the table, ie. contiguous sequence start numbers. You can then use SET IDENTITY INSERT OFF to insert a specific id and reuse a number. The cost of doing so is overwhelming (both runtime and code complexity) compared with the an ordinary identity based insert.
If you really want to reset Identity value to the lowest,
here is the trick you can use through DBCC CHECKIDENT
Basically following sql statements resets identity value so that identity value restarts from the lowest possible number
create table TT (id int identity(1, 1))
GO
insert TT default values
GO 10
select * from TT
GO
delete TT where id between 5 and 10
GO
--; At this point, next ID will be 11, not 5
select * from TT
GO
insert TT default values
GO
--; as you can see here, next ID is indeed 11
select * from TT
GO
--; Now delete ID = 11
--; so that we can reseed next highest ID to 5
delete TT where id = 11
GO
--; Now, let''s reseed identity value to the lowest possible identity number
declare #seedID int
select #seedID = max(id) from TT
print #seedID --; 4
--; We reseed identity column with "DBCC CheckIdent" and pass a new seed value
--; But we can't pass a seed number as argument, so let's use dynamic sql.
declare #sql nvarchar(200)
set #sql = 'dbcc checkident(TT, reseed, ' + cast(#seedID as varchar) + ')'
exec sp_sqlexec #sql
GO
--; Now the next
insert TT default values
GO
--; as you can see here, next ID is indeed 5
select * from TT
GO
I guess we would really need to know why you want to reuse your identity column. The only reason I can think of is because of the temporary nature of your data you might exhaust the possible values for the identity. That is not really likely, but if that is your concern, you can use uniqueidentifiers (guids) as the primary key in your table instead.
The function newid() will create a new guid and can be used in insert statements (or other statements). Then when you delete the row, you don't have any "holes" in your key because guids are not created in that order anyway.
[Syntax assumes SQL2008....]
Yes, it's possible. You need to two management tables, and two triggers on each participating table.
First, the management tables:
-- this table should only ever have one row
CREATE TABLE NextId (Id INT)
INSERT NextId VALUES (1)
GO
CREATE TABLE RecoveredIds (Id INT NOT NULL PRIMARY KEY)
GO
Then, the triggers, two on each table:
CREATE TRIGGER tr_TableName_RecoverId ON TableName
FOR DELETE AS BEGIN
IF ##ROWCOUNT = 0 RETURN
INSERT RecoveredIds (Id) SELECT Id FROM deleted
END
GO
CREATE TRIGGER tr_TableName_AssignId ON TableName
INSTEAD OF INSERT AS BEGIN
DECLARE #rowcount INT = ##ROWCOUNT
IF #rowcount = 0 RETURN
DECLARE #required INT = #rowcount
DECLARE #new_ids TABLE (Id INT PRIMARY KEY)
DELETE TOP (#required) OUTPUT DELETED.Id INTO #new_ids (Id) FROM RecoveredIds
SET #rowcount = ##ROWCOUNT
IF #rowcount < #required BEGIN
DECLARE #output TABLE (Id INT)
UPDATE NextId SET Id = Id + (#required-#rowcount)
OUTPUT DELETED.Id INTO #output
-- this assumes you have a numbers table around somewhere
INSERT #new_ids (Id)
SELECT n.Number+o.Id-1 FROM Numbers n, #output o
WHERE n.Number BETWEEN 1 AND #required-#rowcount
END
SET IDENTITY_INSERT TableName ON
;WITH inserted_CTE AS (SELECT _no = ROW_NUMBER() OVER (ORDER BY Id), * FROM inserted)
, new_ids_CTE AS (SELECT _no = ROW_NUMBER() OVER (ORDER BY Id), * FROM #new_ids)
INSERT TableName (Id, Attr1, Attr2)
SELECT n.Id, i.Attr1, i.Attr2
FROM inserted_CTE i JOIN new_ids_CTE n ON i._no = n._no
SET IDENTITY_INSERT TableName OFF
END
You could script the triggers out easily enough from system tables.
You would want to test this for concurrency. It should work as is, syntax errors notwithstanding: The OUTPUT clause guarantees atomicity of id lookup->increment as one step, and the entire operation occurs within a transaction, thanks to the trigger.
TableName.Id is still an identity column. All the common idioms like $IDENTITY and SCOPE_IDENTITY() will still work.
There is no central table of ids by table, but you could create one easily enough.
I don't have any help for finding the values not in use but if you really want to find them and set them yourself, you can use
set identity_insert on ....
in your code to do so.
I'm with everyone else though. Why bother? Don't you have a business problem to solve?
I've got a trigger attached to a table.
ALTER TRIGGER [dbo].[UpdateUniqueSubjectAfterInsertUpdate]
ON [dbo].[Contents]
AFTER INSERT,UPDATE
AS
BEGIN
-- Grab the Id of the row just inserted/updated
DECLARE #Id INT
SELECT #Id = Id
FROM INSERTED
END
Every time a new entry is inserted or modified, I wish to update a single field (in this table). For the sake of this question, imagine i'm updating a LastModifiedOn (datetime) field.
Ok, so what i've got is a batch insert thingy..
INSERT INTO [dbo].[Contents]
SELECT Id, a, b, c, d, YouDontKnowMe
FROM [dbo].[CrapTable]
Now all the rows are correctly inserted. The LastModifiedOn field defaults to null. So all the entries for this are null -- EXCEPT the first row.
Does this mean that the trigger is NOT called for each row that is inserted into the table, but once AFTER the insert query is finished, ie. ALL the rows are inserted? Which mean, the INSERTED table (in the trigger) has not one, but 'n' number of rows?!
If so .. er.. :( Would that mean i would need a cursor in this trigger? (if i need to do some unique logic to each single row, which i do currently).
?
UPDATE
I'll add the full trigger code, to see if it's possible to do it without a cursor.
BEGIN
SET NOCOUNT ON
DECLARE #ContentId INTEGER,
#ContentTypeId TINYINT,
#UniqueSubject NVARCHAR(200),
#NumberFound INTEGER
-- Grab the Id. Also, convert the subject to a (first pass, untested)
-- unique subject.
-- NOTE: ToUriCleanText just replaces bad uri chars with a ''.
-- eg. an '#' -> ''
SELECT #ContentId = ContentId, #ContentTypeId = ContentTypeId,
#UniqueSubject = [dbo].[ToUriCleanText]([Subject])
FROM INSERTED
-- Find out how many items we have, for these two keys.
SELECT #NumberFound = COUNT(ContentId)
FROM [dbo].[Contents]
WHERE ContentId = #ContentId
AND UniqueSubject = #UniqueSubject
-- If we have at least one identical subject, then we need to make it
-- unique by appending the current found number.
-- Eg. The first instance has no number.
-- Second instance has subject + '1',
-- Third instance has subject + '2', etc...
IF #NumberFound > 0
SET #UniqueSubject = #UniqueSubject + CAST(#NumberFound AS NVARCHAR(10))
-- Now save this change.
UPDATE [dbo].[Contents]
SET UniqueSubject = #UniqueSubject
WHERE ContentId = #ContentId
END
Why not change the trigger to deal with multiple rows?
No cursor or loops needed: it's the whole point of SQL ...
UPDATE
dbo.SomeTable
SET
LastModifiedOn = GETDATE()
WHERE
EXIST (SELECT * FROM INSERTED I WHERE I.[ID] = dbo.SomeTable.[ID]
Edit: Something like...
INSERT #ATableVariable
(ContentId, ContentTypeId, UniqueSubject)
SELECT
ContentId, ContentTypeId, [dbo].[ToUriCleanText]([Subject])
FROM
INSERTED
UPDATE
[dbo].[Contents]
SET
UniqueSubject + CAST(NumberFound AS NVARCHAR(10))
FROM
--Your original COUNT feels wrong and/or trivial
--Do you expect 0, 1 or many rows.
--Edit2: I assume 0 or 1 because of original WHERE so COUNT(*) will suffice
-- .. although, this implies an EXISTS could be used but let's keep it closer to OP post
(
SELECT ContentId, UniqueSubject, COUNT(*) AS NumberFound
FROM #ATableVariable
GROUP BY ContentId, UniqueSubject
HAVING COUNT(*) > 0
) foo
JOIN
[dbo].[Contents] C ON C.ContentId = foo.ContentId AND C.UniqueSubject = foo.UniqueSubject
Edit 2: and again with RANKING
UPDATE
C
SET
UniqueSubject + CAST(foo.Ranking - 1 AS NVARCHAR(10))
FROM
(
SELECT
ContentId, --not needed? UniqueSubject,
ROW_NUMBER() OVER (PARTITION BY ContentId ORDER BY UniqueSubject) AS Ranking
FROM
#ATableVariable
) foo
JOIN
dbo.Contents C ON C.ContentId = foo.ContentId
/* not needed? AND C.UniqueSubject = foo.UniqueSubject */
WHERE
foo.Ranking > 1
The trigger will be run only once for an INSERT INTO query. The INSERTED table will contain multiple rows.
Ok folks, I think I figure it out myself. Inspired by the previous answers and comments, I've done the following. (Can you folks have a quick look over to see if i've over-enginered this baby?)
.1. Created an Index'd View, representing the 'Subject' field, which needs to be cleaned. This is the field that has to be unique .. but before we can make it unique, we need to group by it.
-- Create the view.
CREATE VIEW ContentsCleanSubjectView with SCHEMABINDING AS
SELECT ContentId, ContentTypeId,
[dbo].[ToUriCleanText]([Subject]) AS CleanedSubject
FROM [dbo].[Contents]
GO
-- Index the view with three index's. Custered PK and a non-clustered,
-- which is where most of the joins will be done against.
-- Last one is because the execution plan reakons i was missing statistics
-- against one of the fields, so i added that index and the stats got gen'd.
CREATE UNIQUE CLUSTERED INDEX PK_ContentsCleanSubjectView ON
ContentsCleanSubjectView(ContentId)
CREATE NONCLUSTERED INDEX IX_BlahBlahSnipSnip_A ON
ContentsCleanSubjectView(ContentTypeId, CleanedSubject)
CREATE INDEX IX_BlahBlahSnipSnip_B ON
ContentsCleanSubjectView(CleanedSubject)
.2. Create the trigger code which now
a) grabs all the items 'changed' (nothing new/hard about that)
b) orders all the inserted rows, row numbered with partitioning by a clean subject
c) update the single row we're upto in the main update clause.
here's the code...
ALTER TRIGGER [dbo].[UpdateUniqueSubjectAfterInsertUpdate]
ON [dbo].[Contents]
AFTER INSERT,UPDATE
AS
BEGIN
SET NOCOUNT ON
DECLARE #InsertRows TABLE (ContentId INTEGER PRIMARY KEY,
ContentTypeId TINYINT,
CleanedSubject NVARCHAR(300))
DECLARE #UniqueSubjectRows TABLE (ContentId INTEGER PRIMARY KEY,
UniqueSubject NVARCHAR(350))
DECLARE #UniqueSubjectRows TABLE (ContentId INTEGER PRIMARY KEY,
UniqueSubject NVARCHAR(350))
-- Grab all the records that have been updated/inserted.
INSERT INTO #InsertRows(ContentId, ContentTypeId, CleanedSubject)
SELECT ContentId, ContentTypeId, [dbo].[ToUriCleanText]([Subject])
FROM INSERTED
-- Determine the correct unique subject by using ROW_NUMBER partitioning.
INSERT INTO #UniqueSubjectRows
SELECT SubResult.ContentId, UniqueSubject = CASE SubResult.RowNumber
WHEN 1 THEN SubResult.CleanedSubject
ELSE SubResult.CleanedSubject + CAST(SubResult.RowNumber - 1 AS NVARCHAR(5)) END
FROM (
-- Order all the cleaned subjects, partitioned by the cleaned subject.
SELECT a.ContentId, a.CleanedSubject, ROW_NUMBER() OVER (PARTITION BY a.CleanedSubject ORDER BY a.ContentId) AS RowNumber
FROM ContentsCleanSubjectView a
INNER JOIN #InsertRows b ON a.ContentTypeId = b.ContentTypeId AND a.CleanedSubject = b.CleanedSubject
GROUP BY a.contentId, a.cleanedSubject
) SubResult
INNER JOIN [dbo].[Contents] c ON c.ContentId = SubResult.ContentId
INNER JOIN #InsertRows d ON c.ContentId = d.ContentId
-- Now update all the effected rows.
UPDATE a
SET a.UniqueSubject = b.UniqueSubject
FROM [dbo].[Contents] a INNER JOIN #UniqueSubjectRows b ON a.ContentId = b.ContentId
END
Now, the subquery correctly returns all the cleaned subjects, partitioned correctly and numbered correctly. I never new about the 'PARTITION' command, so that trick was the big answer here :)
Then i just join'd the subquery with the row that is being updated in the parent query. The row number is correct, so now i just do a case. if this is the first time the cleaned subject exists (eg. row_number = 1), don't modify it. otherwise, append the row_number minus one. This means the 2nd instance of the same subject, the unique subject will be => cleansubject + '1'.
The reason why i believe i need to have an index'd view is because if i have two very similar subjects, that when you have stripped out (ie. cleaned) all the bad chars (which i've determined are bad) .. it's possible that the two clean subjects are the same. As such, I need to do all my joins on a cleanedSubject, instead of a subject. Now, for the massive amount of rows I have, this is crap for performance when i don't have the view. :)
So .. is this over engineered?
Edit 1:
Refactored trigger code so it's waay more performant.