I need to create or, if it is exists, change default value for an existing column at table users.
I found how can i create/set default value for that column at this link: How to set a default value for an existing column
But I need a conditional statement. I mean, if a default value exists, it should be changed, if not, it should be created.
Which query do I need to execute for this problem?
You can't modify a default value, the single way is to drop first the constraint:
IF EXISTS (SELECT * FROM dbo.sysobjects WHERE id = OBJECT_ID(N'[DF_someName]') AND type = 'D')
BEGIN
ALTER TABLE [dbo].[users] DROP CONSTRAINT [DF_someName]
END
and you create the new one :
ALTER TABLE [dbo].[users] ADD CONSTRAINT [DF_someName] DEFAULT N'NewValue' FOR [columnName]
You don't. You determine if a default constraint exists using something like this and drop it if it does. Then you add the default constraint that you need.
Related
I have a table abc in mssql which has column xyz which has its default has been set to not null, so the insert query fails when it has null value, I need help to change the default so that it accepts null values, table has only one constraint and its not on the column that I want to modify .
ALTER TABLE xyz
ALTER COLUMN xyz NVARCHAR(10) NULL
Alter should work fine here, obviously change NVARCHAR(10) to whatever type you need
According to (How to set a default value for an existing column)
You have 2 options:
1. Setting a constraint:
ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn;
Add Default:
ALTER TABLE Employee ADD DEFAULT 'SANDNES' FOR CityBorn
I'm working with my first database and already have a problem. I have several tables. Some of them have PK set to autoincrement, others have nvarchar() type.
I have created trigger, which update or insert value into cell. This trigger works when I manually insert value for PF, in my case for nvarchar() values. It is not working for PK, where is set to autoincrement - int. I need help to create trigger which will work for that typs.
Example of trigger:
ALTER TRIGGER [dbo].[Table_Name_trigger_update]
ON [dbo].[Table_Name]
AFTER UPDATE
AS
BEGIN
UPDATE Table_Name
SET
changed_date = getdate()
, changed_user = CURRENT_USER
FROM inserted AS ij
WHERE ij.ID_name = Table_Name.ID_name
RETURN
END
So as I write earlier, this work on nvarchar(), where I manually insert PK. In that case trigger update the getdate() and CURRENT_USER value in table.
You don't need this trigger actually.
Try to replace it with these Default Constraints:
ALTER TABLE Table_Name ADD DEFAULT (getdate()) FOR changed_date
GO
ALTER TABLE Table_Name ADD DEFAULT (CURRENT_USER) FOR changed_user
GO
You can solve this without a trigger as #GriGrim already stated. But i would suggest another solution:
ALTER TABLE Table_Name ADD DEFAULT (getdate()) FOR changed_date
GO
ALTER TABLE Table_Name ADD DEFAULT (SUSER_SNAME()) FOR changed_user
GO
You can compare the results using this:
SELECT CURRENT_USER, SUSER_SNAME()
CURRENT_USER tends to return dbo not the real username.
This isn't working in SQL Server 2008:
ALTER TABLE Employee ALTER COLUMN CityBorn SET DEFAULT 'SANDNES'
The error is:
Incorrect syntax near the keyword 'SET'.
What am I doing wrong?
This will work in SQL Server:
ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn;
ALTER TABLE Employee ADD DEFAULT 'SANDNES' FOR CityBorn
cannot use alter column for that, use add instead
ALTER TABLE Employee
ADD DEFAULT('SANDNES') FOR CityBorn
The correct way to do this is as follows:
Run the command:
sp_help [table name]
Copy the name of the CONSTRAINT.
Drop the DEFAULT CONSTRAINT:
ALTER TABLE [table name] DROP [NAME OF CONSTRAINT]
Run the command below:
ALTER TABLE [table name] ADD DEFAULT [DEFAULT VALUE] FOR [NAME OF COLUMN]
Hoodaticus's solution was perfect, thank you, but I also needed it to be re-runnable and found this way to check if it had been done...
IF EXISTS(SELECT * FROM information_schema.columns
WHERE table_name='myTable' AND column_name='myColumn'
AND Table_schema='myDBO' AND column_default IS NULL)
BEGIN
ALTER TABLE [myDBO].[myTable] ADD DEFAULT 0 FOR [myColumn] --Hoodaticus
END
There are two scenarios where default value for a column could be changed,
At the time of creating table
Modify existing column for a existing table.
At the time of creating table / creating new column.
Query
create table table_name
(
column_name datatype default 'any default value'
);
Modify existing column for a existing table
In this case my SQL server does not allow to modify existing default constraint value. So to change the default value we need to delete the existing system generated or user generated default constraint. And after that default value can be set for a particular column.
Follow some steps :
List all existing default value constraints for columns.
Execute this system database procedure, it takes table name as a parameter. It returns list of all constrains for all columns within table.
execute [dbo].[sp_helpconstraint] 'table_name'
Drop existing default constraint for a column.
Syntax:
alter table 'table_name' drop constraint 'constraint_name'
Add new default value constraint for that column:
Syntax:
alter table 'table_name' add default 'default_value' for 'column_name'
cheers #!!!
First drop constraints
https://stackoverflow.com/a/49393045/2547164
DECLARE #ConstraintName nvarchar(200)
SELECT #ConstraintName = Name FROM SYS.DEFAULT_CONSTRAINTS
WHERE PARENT_OBJECT_ID = OBJECT_ID('__TableName__')
AND PARENT_COLUMN_ID = (SELECT column_id FROM sys.columns
WHERE NAME = N'__ColumnName__'
AND object_id = OBJECT_ID(N'__TableName__'))
IF #ConstraintName IS NOT NULL
EXEC('ALTER TABLE __TableName__ DROP CONSTRAINT ' + #ConstraintName)
Second create default value
ALTER TABLE [table name] ADD DEFAULT [default value] FOR [column name]
ALTER TABLE [dbo].[Employee] ADD DEFAULT ('N') FOR [CityBorn]
in case a restriction already exists with its default name:
-- Drop existing default constraint on Employee.CityBorn
DECLARE #default_name varchar(256);
SELECT #default_name = [name] FROM sys.default_constraints WHERE parent_object_id=OBJECT_ID('Employee') AND COL_NAME(parent_object_id, parent_column_id)='CityBorn';
EXEC('ALTER TABLE Employee DROP CONSTRAINT ' + #default_name);
-- Add default constraint on Employee.CityBorn
ALTER TABLE Employee ADD CONSTRAINT df_employee_1 DEFAULT 'SANDNES' FOR CityBorn;
You can use following syntax, For more information see this question and answers : Add a column with a default value to an existing table in SQL Server
Syntax :
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES
Example :
ALTER TABLE SomeTable
ADD SomeCol Bit NULL --Or NOT NULL.
CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is
autogenerated.
DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.
Another way :
Right click on the table and click on Design,then click on column that you want to set default value.
Then in bottom of page add a default value or binding : something like '1' for string or 1 for int.
Just Found 3 simple steps to alter already existing column that was null before
update orders
set BasicHours=0 where BasicHours is null
alter table orders
add default(0) for BasicHours
alter table orders
alter column CleanBasicHours decimal(7,2) not null
Try following command;
ALTER TABLE Person11
ADD CONSTRAINT col_1_def
DEFAULT 'This is not NULL' FOR Address
ALTER TABLE tblUser
ADD CONSTRAINT DF_User_CreatedON DEFAULT GETDATE() FOR CreatedOn
Like Yuck's answer with a check to allow the script to be ran more than once without error. (less code/custom strings than using information_schema.columns)
IF object_id('DF_SomeName', 'D') IS NULL BEGIN
Print 'Creating Constraint DF_SomeName'
ALTER TABLE Employee ADD CONSTRAINT DF_SomeName DEFAULT N'SANDNES' FOR CityBorn;
END
I have a table [Product] with a column [CreateTime] datetime null, and is has some data already.
How can I set the column [CreateTime] 's default value to getdate(), and make the new added data to have a default value getdate() for column [CreateTime].
You cannot change a default - you will need to first drop it, and then recreate it.
In order to drop it, you need to know its name, and then use
ALTER TABLE dbo.Product
DROP CONSTRAINT yourOldDefaultConstraint
Once you've done that, you can add a new default constraint, and in order to apply it to existing rows, use the "WITH VALUES" part:
ALTER TABLE dbo.Product
ADD CONSTRAINT NewDefaultConstraintName
DEFAULT GetDate() FOR CreateTime WITH VALUES
Oops - sorry, the "WITH VALUES" only seems to work if you create a DEFAULT constraint at the time you create the table, or if you add the column - it doesn't seem to get applied to an existing column.
In this case you would just have to follow your ALTER TABLE statement with something like this:
UPDATE dbo.T_Product
SET CreateTime = GETDATE()
WHERE CreateTime IS NULL
That should do the trick, too!
Marc
In SQL Server 2000/2005,
Is it possible to force the default value to be written to already existing rows when adding a new column to a table without using NOT NULL on the new column?
You need two statements. First create the column with not null. Then change the not null constraint to nullable
alter table mytable add mycolumn varchar(10) not null default ('a value')
alter table mytable alter column mycolumn varchar(10) null
I understand your question, but you are saying that for future records, NULL (unknown, indeterminate or whatever your semantics are) is acceptable (but if it is left off in an insert, there will be a default), but that for all the existing data, you are going to go ahead and assign it the default.
I would have to look hard at this situation and ask why you are even going to allow NULLs in future records at all - given none of the historical records will have it, and there is a default in place for future records.
I doubt it.
http://msdn.microsoft.com/en-us/library/ms190273(SQL.90).aspx
The approach recommended by Microsoft is as follows (taken from the url above)
UPDATE MyTable SET NullCol = N'some_value' WHERE NullCol IS NULL
ALTER TABLE MyTable ALTER COLUMN NullCOl NVARCHAR(20) NOT NULL
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
[**WITH VALUES]**
WITH VALUES can be used to store the default value in the new column for each existing row in the table.
more detail on MSDN link .
https://msdn.microsoft.com/en-in/library/ms190273.aspx