In my database in a sql-server 2005 instance, I need to add a new column to a table with existing data. The table currently looks like this:
CREATE TABLE [dbo].[Status](
[Status_ID] [int] IDENTITY(1,1) NOT NULL,
[Description] [nvarchar](80) COLLATE Latin1_General_CI_AS NOT NULL
)
The column I want to add is also of type INT and nulls are not allowed. Furthermore, I want the initial values for this column to be equal to the ID (it cannot be a computed column).
This is the script I have written for this:
ALTER TABLE [dbo].[Status]
add Status_Code int NOT NULL DEFAULT 1
GO
//Get the number of rows
DECLARE #RowCount INT
SET #RowCount = (SELECT COUNT(Status_ID) FROM Status)
//Create an iterator
DECLARE #I INT
SET #I = 1
//Loop through the rows of a table #myTable
WHILE (#I <= #RowCount)
BEGIN
UPDATE Status
SET Status_Code = #I
WHERE Status_ID = #I
//Increment the iterator
SET #I = #I + 1
END
This script seems to work perfectly. However, it seems like a lot of code for a rather small task. Does anyone know of a more efficient way to code this?
Why loop through the table to do the update? Just do this:
ALTER TABLE [dbo].[Status]
add Status_Code int NOT NULL DEFAULT 1
UPDATE Status
SET Status_Code = Status_ID
Create the new column, and make it nullable.
Then write a simple update statement to insert the existing id's into the new columns.
Then make your column not-nullable.
I would go with Gerrie's answer as you want the column to be NOT NULL. If you specify a default value, SQL server will still allow you to leave out that column in any subsequent insert statement (the column will be assigned the default value)
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
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
SQL Server is causing an error when I try to insert values at the same time to multiple rows one after another. So basically, I have created following table and query
create table Dates
(
id int not null primary key,
dates DateTime Not Null Default(GetDate())
)
declare #i int
set #i = ##ROWCOUNT + 1
insert into dbo.Dates(id)
values (#i + 1)
select * from Dates
When I run second query repeatedly, this error happens:
Violation of PRIMARY KEY constraint 'PK__Dates__3213E83F76720BE7'. Cannot insert duplicate key in object 'dbo.Dates'. The duplicate key value is (3).
The statement has been terminated.
Why it is this error showing up? I am creating a form, information will be stored in SQL Server and I do not want this to happen. What can I do? Thank you.
Use identity that will generate next value for your column automatically
create table Dates (
id int identity(1,1) primary key,
dates DateTime Not Null Default(GetDate())
)
You want to use IDENTITY. No need to do this manually.
In your case, ##ROWCOUNT doesn't change hence you get duplicate keys...
Statements that make a simple assignment always set the ##ROWCOUNT value to 1. No rows are sent to the client. Examples of these statements are: SET #local_variable, RETURN, READTEXT, and select without query statements such as SELECT GETDATE() or SELECT 'Generic Text'.
declare #i int
set #i=##ROWCOUNT+1
select #i
set #i = ##ROWCOUNT+1
select #i
The expression #i+1 in the insert statement will always return the same value. It doesn't increment the value of variable #i. That's why there is an error. Put insert statement inside a loop and use statement set #i = #i + 1 to increment the value of #i inside the loop.
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 .
I have a situation where a table has three columns ID, Value and status. For a distinct ID there should be only one status with value 1 and it should be allowed for ID to have more then one status with value 0. Unique key would prevent ID of having more then one status (0 or 1).
Is there a way to solve this, maybe using constraints?
Thanks
You can create an indexed view that will uphold your constraint of keeping ID unique for [Status] = 1.
create view dbo.v_YourTable with schemabinding as
select ID
from dbo.YourTable
where [Status] = 1
go
create unique clustered index UX_v_UniTest_ID on v_YourTable(ID)
In SQL Server 2008 you could use a unique filtered index instead.
If the table can have duplicate ID values, then a check constraint wouldn't work for your situation. I think the only way would be to use a trigger. If you are looking for an example then I can post one. But in summary, use a trigger to test if the inserted/updated ID has a status of 1 that is duplicated across the same ID.
EDIT: You could always use a unique constraint on ID and Value. I'm thinking that will give you what you are looking for.
You could put this into an insert/ update trigger to check to make sure only one combination exists with the 1 value; if your condition is not met, you could throw a trappable error and force the operation to roll back.
If you can use NULL instead of 0 for a zero-status, then you can use a UNIQUE constraint on the pair and it should work. Since NULL is not an actual value (NULL != NULL), then rows with multiple nulls should not conflict.
IMHO, this basically is a normalisation problem. The column named "id" does not uniquely address a row, so it can never be a PK. At least a new (surrogate) key(element) is needed. The constraint itself cannot be expressed as an expression "within the row", so it has to be expressed in terms of a FK.
So it breaks down into two tables:
One with PK=id, and a FK REFERENCING two.sid
Two with PK= surrogate key, and FK id REFERENCING one.id
The original payload "value" also lives here.
The "one bit variable" disappears, because it can be expressed in terms of EXISTS. (effectively table one points to the row that holds the token)
[I expect the Postgres rule system could be used to use the above two-tables-model to emulate the intended behaviour of the OP. But that would be an ugly hack...]
EDIT/UPDATE:
Postgres supports partial/conditional indices. (don't know about ms-sql)
DROP TABLE tmp.one;
CREATE TABLE tmp.one
( sid INTEGER NOT NULL PRIMARY KEY -- surrogate key
, id INTEGER NOT NULL
, status INTEGER NOT NULL DEFAULT '0'
/* ... payload */
);
INSERT INTO tmp.one(sid,id,status) VALUES
(1,1,0) , (2,1,1) , (3,1,0)
, (4,2,0) , (5,2,0) , (6,2,1)
, (7,3,0) , (8,3,0) , (9,3,1)
;
CREATE UNIQUE INDEX only_one_non_zero ON tmp.one (id)
WHERE status > 0 -- "partial index"
;
\echo this should succeed
BEGIN ;
UPDATE tmp.one SET status = 0 WHERE sid=2;
UPDATE tmp.one SET status = 1 WHERE sid=1;
COMMIT;
\echo this should fail
BEGIN ;
UPDATE tmp.one SET status = 1 WHERE sid=4;
UPDATE tmp.one SET status = 0 WHERE sid=9;
COMMIT;
SELECT * FROM tmp.one ORDER BY sid;
I came up with a solution
First create a function
CREATE FUNCTION [dbo].[Check_Status] (#ID int)
RETURNS INT
AS
BEGIN
DECLARE #r INT;
SET #r =
(SELECT SUM(status) FROM dbo.table where ID= #ID);
RETURN #r;
END
Second create a constraint in table
([dbo].[Check_Status]([ID])<(2))
In this way one ID could have single status (1) and as many as possible status (0).
create function dbo.IsValueUnique
(
#proposedValue varchar(50)
,#currentId int
)
RETURNS bit
AS
/*
--EXAMPLE
print dbo.IsValueUnique() -- fail
print dbo.IsValueUnique(null) -- fail
print dbo.IsValueUnique(null,1) -- pass
print dbo.IsValueUnique('Friendly',1) -- pass
*/
BEGIN
DECLARE #count bit
set #count =
(
select count(1)
from dbo.MyTable
where #proposedValue is not null
and dbo.MyTable.MyPkColumn != #currentId
and dbo.MyTable.MyColumn = #proposedValue
)
RETURN case when #count = 0 then 1 else 0 end
END
GO
ALTER TABLE MyTable
WITH CHECK
add constraint CK_ColumnValueIsNullOrUnique
CHECK ( 1 = dbo.IsValueNullOrUnique([MyColumn],[MyPkColumn]) )
GO