I'm preventing the user from adding the same surname in the list in the code array below. But my goal is to check all the lines using the 'trigger'. As a result: what do I need to do to check all the columns?
In summary: Check all columns. If the same value is entered, prevent it from being added.
ALTER TRIGGER trigger_example
ON dbo.information
INSTEAD OF INSERT
AS
DECLARE #surname varchar(30)
select #surname = Person_Job FROM inserted
IF(#surname = 'Enderson')
BEGIN
PRINT 'The person with this record already exists in the list.'
END
ELSE
BEGIN
INSERT INTO personel.dbo.information(Person_id,Person_FirstName,Person_LastName,Person_Salary,Person_Job)
SELECT Person_id,Person_FirstName,Person_LastName,Person_Salary,Person_Job FROM inserted
END
GO
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mark the column as unique
add up a constraint:
unique
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
I have a table named WORD with the following columns
WORD_INDEX INT NOT NULL AUTO_INCREMENT,
CONTENT VARCHAR(255),
FREQUENCY INT
What I want to do is when I try to add a row to the table if a row with the same CONTENT exits, I want to increment the FREQUENCY by 1. Otherwise I want to add the row to the table. And then the WORD_INDEX in the newly inserted row or updated row must be returned.
I want to do this in H2 database from one query.
I have tried 'on duplicate key update', but this seems to be not working in H2.
PS- I can do this with 1st making a select query with CONTENT and if I get a empty result set, makeing insert query and otherwise making a update query. But as I have a very large number of words, I am trying to optimize the insert operation. So what I am trying to do is reducing the database interactions I am making.
Per your edited question .. you can achieve this using a stored procedure like below [A sample code]
DELIMITER $$
create procedure sp_insert_update_word(IN CONTENT_DATA VARCHAR(255),
IN FREQ INT, OUT Insert_Id INT)
as
begin
declare #rec_count int;
select #rec_count = count(*) from WORD where content = CONTENT_DATA;
IF(#rec_count > 0) THEN
UPDATE WORD SET FREQUENCY = FREQUENCY + 1 where CONTENT = CONTENT_DATA;
SELECT NULL INTO Insert_Id;
else
INSERT INTO WORD(CONTENT, FREQUENCY) VALUES(CONTENT_DATA, FREQ);
SELECT LAST_INSERT_ID() INTO Insert_Id;
END IF;
END$$
DELIMITER ;
Then call your procedure and select the returned inserted id like below
CALL sp_insert_update_word('some_content_data', 3, #Insert_Id);
SELECT #Insert_Id;
The above procedure code essentially just checking that, if the same content already exists then perform an UPDATE otherwise perform an INSERT. Finally return the newly generated auto increment ID if it's insert else return null.
First try to update frequency where content = "your submitted data here". If the affected row = 0 then insert a new row. You also might want make CONTENT unique considering it will always stored different data.
Here is a trigger
CREATE TRIGGER [dbo].[CheckApplyId]
ON [dbo].[AppliedStudent_event] INSTEAD OF INSERT
AS
DECLARE #studentId INT
DECLARE #compReq_Id INT
BEGIN
SELECT #studentId = studentId
FROM INSERTED
SELECT #compReq_Id = compReq_Id
FROM INSERTED
IF EXISTS(SELECT StudentId,
compreq_id
FROM AppliedStudent_event
WHERE StudentId = #studentId
AND compreq_id = #compReq_Id)
BEGIN
ROLLBACK
PRINT 'User Already Applied'
END
END
When in insert a data into a table using command:
INSERT INTO AppliedStudent_event (StudentId, compreq_id)
VALUES (3026, 1)
Message is:
(1 row(s) affected)
But when I execute a sql command no data is inserted in the table.
Can you please tell why are you using trigger because you use only assign the variable #studentId and #compReq_Id from inserted table.
That's a broken trigger because inserted can contain multiple (or no) rows - so a statement like SELECT #ScalarVariable = column from inserted is always wrong.
And it's unnecessary since you can just place a UNIQUE constraint on the StudentId and compreq_id columns:
ALTER TABLE AppliedStudent_event
ADD CONSTRAINT UQ_Student_Events
UNIQUE (StudentId,compreq_id)
And it's further broken because you've specified it as an instead of trigger - that says that your code is going to be responsible for the actual insert - but your code doesn't actually do that. That's why no data ends up in the table.
If you insist on doing it as a trigger, it's actually tricky to get everything correct (that's why I'd really recommend the UNIQUE constraint). It'll end up being something like this:
CREATE TRIGGER [dbo].[CheckApplyId]
ON [dbo].[AppliedStudent_event] INSTEAD OF INSERT
AS
IF EXISTS(select
StudentId,compreq_id,COUNT(*)
from inserted
group by StudentId,compreq_id
HAVING COUNT(*) > 1)
OR EXISTS (select *
from inserted i
inner join
AppliedStudent_event e
on
i.StudentId = e.StudentId and
i.compreq_id = e.compreq_id)
BEGIN
ROLLBACK
PRINT 'User Already Applied'
END
ELSE
BEGIN
INSERT INTO AppliedStudent_event(StudentId,compreq_id /* Other columns? */)
SELECT StudentId,compreq_id /* And again, other columns */
FROM inserted
END
I use this code to check if an element of the new entry is equal to an element of previously inserted data.
CREATE TRIGGER trig1 ON Table1
AFTER INSERT
AS
DECLARE trigcursor CURSOR FOR
SELECT Name FROM INSERTED
DECLARE #Name1 varchar(80)
OPEN trigcursor;
FETCH NEXT FROM trigcursor INTO #Name1
WHILE ##FETCH_STATUS = 0
BEGIN
IF EXISTS(SELECT * FROM Table1 WHERE Name= #Name1)
BEGIN
...
END
FETCH NEXT FROM trigcursor INTO #Name1
END
The problem is that for some reason the new entry exists also in the table Table1, not only in INSERTED. So the condition is always true. Can you help me why this happens? Is there a way to retrieve only the initial table without the new entry in it? Thanks!
Your trigger is AFTER INSERT on table Table1. It should be BEFORE INSERT if you expect not to find the record in the table.
Alternative: use INSTEAD OF INSERT trigger.
OR
Add another column that accepts null. Make it a number column so that it will be fast. Do not insert any value in it on the insert. Then, in the AFTER INSERT TRIGGER, the rows that have that column empty are the new ones. The ones that have the column filled with something are the old ones.
Then update empty columns with value.
eg: add column mark
After insert, look for the name:
SELECT * FROM Table1 WHERE Name= #Name1 and mark is not null
Once you found out whether or not it existed before, update everything with something:
update table1 set mark = 1 where mark is null
We have a user table, every user has an unique email and username. We try to do this within our code but we want to be sure users are never inserted (or updated) in the database with the same username of email.
I've added a BEFORE INSERT Trigger which prevents the insertion of duplicate users.
CREATE TRIGGER [dbo].[BeforeUpdateUser]
ON [dbo].[Users]
INSTEAD OF INSERT
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
DECLARE #Email nvarchar(MAX)
DECLARE #UserName nvarchar(MAX)
DECLARE #UserId int
DECLARE #DoInsert bit
SET #DoInsert = 1
SELECT #Email = Email, #UserName = UserName FROM INSERTED
SELECT #UserId = UserId FROM Users WHERE Email = #Email
IF (#UserId IS NOT NULL)
BEGIN
SET #DoInsert = 0
END
SELECT #UserId = UserId FROM Users WHERE UserName = #UserName
IF (#UserId IS NOT NULL)
BEGIN
SET #DoInsert = 0
END
IF (#DoInsert = 1)
BEGIN
INSERT INTO Users
SELECT
FirstName,
LastName,
Email,
Password,
UserName,
LanguageId,
Data,
IsDeleted
FROM INSERTED
END
ELSE
BEGIN
DECLARE #ErrorMessage nvarchar(MAX)
SET #ErrorMessage =
'The username and emailadress of a user must be unique!'
RAISERROR 50001 #ErrorMessage
END
END
But for the Update trigger I have no Idea how to do this.
I've found this example with google:
http://www.devarticles.com/c/a/SQL-Server/Using-Triggers-In-MS-SQL-Server/2/
But I don't know if it applies when you update multiple columns at once.
EDIT:
I've tried to add a unique constraint on these columns but it doesn't work:
Msg 1919, Level 16, State 1, Line 1
Column 'Email' in table 'Users' is of a type
that is invalid for use as a key column in an index.
You can add a unique contraint on the table, this will raise an error if you try and insert or update and create duplicates
ALTER TABLE [Users] ADD CONSTRAINT [IX_UniqueUserEmail] UNIQUE NONCLUSTERED
(
[Email] ASC
)
ALTER TABLE [Users] ADD CONSTRAINT [IX_UniqueUserName] UNIQUE NONCLUSTERED
(
[UserName] ASC
)
EDIT: Ok, i've just read your comments to another post and seen that you're using NVARCHAR(MAX) as your data type. Is there a reason why you might want more than 4000 characters for an email address or username? This is where your problem lies. If you reduce this to NVARCHAR(250) or thereabouts then you can use a unique index.
Sounds like a lot of work instead of just using one or more unique indexes. Is there a reason you haven't gone the index route?
Why not just use the UNIQUE attribute on the column in your database? Setting that will make the SQL server enforce that and throw an error if you try to insert a dupe.
You should use a SQL UNIQUE constraint on each of these columns for that.
You can create a UNIQUE INDEX on an NVARCHAR as soon as it's an NVARCHAR(450) or less.
Do you really need a UNIQUE column to be so large?
In general, I would avoid Triggers wherever possible as they can make the behaviour very hard to understand unless you know that the trigger exists. As other commentatators have said, a unique constraint is the way to go (once you have amended your column definitions to allow it).
If you ever find yourself needing to use a trigger, it may be a sign that your design is flawed. Think hard about why you need it and whether it is performing logic that belongs elsewhere.
Be aware that if you use the UNIQUE constraint/index solution with SQL Server, only one null value will be permitted in that column. So, for example, if you wanted the email address to be optional, it wouldn't work, because only one user could have a null email address. In that case, you would have to resort to another approach like a trigger or a filtered index.