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
Related
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
I use SQL Server 2016. I have a database table called "Member".
In that table, I have these 3 columns (for the purpose of my question):
idMember [INT - Identity - Primary Key]
memEmail
memEmailPartner
I want to prevent a row to use an email that already exists in the table.
Both email columns are not mandatory, so they can be left blank (NULL).
If I create a new Member:
If not blank, the values entered for "memEmail" and "memEmailPartner" (independently) should not be found in any other rows in columns memEmail nor memEmailPartner.
So if I want to create a row with email (dominic#email.com) I must not find any occurrences of that value in memEmail or memEmailPartner.
If I update an existing Member:
I must not find any occurrences of that value in memEmail or memEmailPartner, with the exception that I am updating the row (idMembre) which already have the value in memEmail or memEmailPartner.
--
From what I read on Google, it should be possible to do something with a Function-Based Check Constraint but I can't make that work.
Anyone have a solution to my problem ?
Thank you.
I may have misunderstood exactly what you were asking but it looks like you want a simple upsert query with IF EXISTS conditions.
DECLARE #emailAddress VARCHAR(255)= 'dominic#email.com', --dummy value
#id INT= 2; --dummy value
IF NOT EXISTS
(
SELECT 1
FROM #Member
WHERE memEmail = #emailAddress
OR memEmailPartner = #emailAddress
)
BEGIN
SELECT 'insert';
END;
ELSE IF EXISTS
(
SELECT 1
FROM #Member
WHERE idMember = #id
)
BEGIN
SELECT 'update';
END;
A trigger is the traditional way of doing doing what you're asking for. Here's a simple demo;
--if object_id('member') is not null drop table member
go
create table member (
idMember INT Identity Primary Key,
memEmail varchar(100),
memEmailPartner varchar(100)
)
go
create trigger trg_member on member after insert, update as
begin
set nocount on
if exists (select 1 from member m join inserted i on i.memEmail = m.memEmail and i.idMember <> m.idMember) or
exists (select 1 from member m join inserted i on i.memEmail = m.memEmailPartner and i.idMember <> m.idMember) or
exists (select 1 from member m join inserted i on i.memEmailPartner = m.memEmail and i.idMember <> m.idMember) or
exists (select 1 from member m join inserted i on i.memEmailPartner = m.memEmailPartner and i.idMember <> m.idMember)
begin
raiserror('Email addresses must be unique.', 16, 1)
rollback
end
end
go
insert member(memEmail, memEmailPartner) values('a#a.com', null), ('b#b.com', null), (null, 'c#c.com'), (null, 'd#d.com')
go
select * from member
insert member(memEmail, memEmailPartner) values('a#a.com', null) -- should fail
go
insert member(memEmail, memEmailPartner) values(null, 'a#a.com') -- should fail
go
insert member(memEmail, memEmailPartner) values('c#c.com', null) -- should fail
go
insert member(memEmail, memEmailPartner) values(null, 'c#c.com') -- should fail
go
insert member(memEmail, memEmailPartner) values('e#e.com', null) -- should work
go
insert member(memEmail, memEmailPartner) values(null, 'f#f.com') -- should work
go
select * from member
-- Make sure updates still work!
update member set memEmail = memEmail, memEmailPartner = memEmailPartner
I've not tested this extensively but it should be enough to get you started if you want to try this approach.
StuartLC notes the potential for the UDF check constraint to fail in set based updates and/or various other conditions, triggers don't have this problem.
Stuart also suggests reconsidering whether this should really be a database constraint or managed through business logic elsewhere. I'm inclined to agree - my gut feel here is that sooner or later you will come across a situation that requires email addresses to be reused, or in some other way not strictly unique.
TL;DR
The wisdom of applying this kind of business rule logic in the database needs to be reconsidered - this check is likely a better candidate for your application, or a stored procedure which acts as an insert gate keeper instead of direct new row inserts into the table.
Ignoring the Warnings
That said, I do believe that what you want is however possible in a constraint UDF, albeit with potentially atrocious performance consequences*1, and likely prone to race conditions in set based updates
Here's a user defined function which applies the unique email logic across both columns. Note that by the time the constraint is checked, that the row is IN the table already, hence the new row itself needs to be excluded from the duplicate checks.
My code also is depedent on ANSI NULL behaviour, i.e. that the predicates NULL = NULL and X IN (NULL) both return NULL, and hence are excluded from the failure check (in order to meet your requirement that NULLS do not fail the rule).
We also need to check for the insert of BOTH new columns being non-null, but duplicated.
So here's the a UDF doing the checking:
CREATE FUNCTION dbo.CheckUniqueEmails(#id int, #memEmail varchar(50),
#memEmailPartner varchar(50))
RETURNS bit
AS
BEGIN
DECLARE #retval bit;
IF #memEmail = #memEmailPartner
OR EXISTS (SELECT 1 FROM MyTable WHERE memEmail IS NOT NULL
AND memEmail IN(#memEmail, #memEmailPartner) AND idMember <> #id)
OR EXISTS (SELECT 1 FROM MyTable WHERE memEmailPartner IS NOT NULL
AND memEmailPartner IN(#memEmail, #memEmailPartner) AND idMember <> #id)
SET #retval = 0
ELSE
SET #retval = 1;
RETURN #retval;
END;
GO
Which is then enforced in a CHECK constraint:
ALTER TABLE MyTable ADD CHECK (dbo.CheckUniqueEmails(
idMember, memEmail, memEmailPartner) = 1);
I've put a SQLFiddle up here
Uncomment the 'failed' test cases to ensure that the above check constraint is working.
I haven't tested this with updates, and as per Martin's advice on the link, this will likely break on an insert with multiple rows.
*1 - we'll need indexes on BOTH email address columns.
I'm a novice when it comes to Stored Procedures in SQL Server Management Studio. I have an application that I was told to make the following changes to using a stored procedure:
Step 1. User types in an item number.
Step 2. Customer name, address, etc. displays in the other fields on the same form.
There are 3 tables: Bulk orders, Small orders, and Customer information.
Bulk orders and small orders are in Database_1 and Customer information is in Database_2.
The primary key for small orders is the order number. A column in small orders contains the customer number for each order. That customer number is the primary key in the customer table.
The bulk orders table is similar.
I want to include a conditional statement that says: if order number is found in small orders table, show data from customer table that coorelates with that order number. I've attempted this multiple ways, but keep getting a "The multi-part identifier.... could not be bound" error.
I.E:
SELECT DB1.db.Customer_Table.Customer_Column AS CustomerNumber;
IF(CustomerNumber NOT LIKE '%[a-z]%')
BEGIN
SELECT * FROM db.small_orders_table;
END
ELSE
BEGIN
SELECT * FROM db.buld_orders_table;
END
Please help.
Sounds like it's 2 databases on the same server...in that case, you'll need to specify the fully qualified table name (database.schema.table) when referencing a table on the other database from where your stored procedure is found.
Database_1.db.small_orders_tables
first of all, you cannot use aliases as variables. If you want to assign a value to a variable in order to test it, you have to do a SELECT statement like SELECT #var = DB1.db.Customer_Table.Customer_Column FROM <YourTableFullName> WHERE <condition>. Then you can use the #var (which must be declared before) for your test.
About the error you're experiencing, youre using fully qualified names in a wrong way. If you're on the same server (different databases), you need to specify just the database name on the top and then the schema of your objects. Suppose to have the following database objects on the Database1:
USE Database1;
GO
CREATE TABLE dbo.Table1
(
id int IDENTITY(1, 1) NOT NULL PRIMARY KEY CLUSTERED
, val varchar(30)
);
GO
INSERT INTO dbo.Table1 (val) VALUES ('test1');
GO
INSERT INTO dbo.Table1 (val) VALUES ('test2');
GO
INSERT INTO dbo.Table1 (val) VALUES ('test3');
GO
And the following ones on Database2:
USE Database2;
GO
CREATE TABLE dbo.Table2
(
id int IDENTITY(1, 1) NOT NULL PRIMARY KEY CLUSTERED
, val varchar(30)
);
GO
Now, suppose that you want to read from the first table the value with id = 2, and then to apply your IF. Let's declare a variable and test it:
USE Database1;
GO
DECLARE #var varchar(30);
-- since you're on Database1, you don't need to specify full name
SELECT #var = val FROM dbo.Table1 WHERE id = 2;
IF #var = 'test2'
BEGIN
SELECT id, val FROM dbo.Table1;
END
ELSE
BEGIN
-- in this case the database name is needed
SELECT id, val FROM Database2.dbo.Table2;
END
GO
Does it help?
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?