I have the following working SQL query that adds a constraint MindestensEinKontakt_CHECK to the table KundenKontaktDaten. The constrainst ensures that at least one of the attributes Twitter_Id, Google_Id, Facebook_Id, Skype_Id, and Telefonnummer is not null:
ALTER TABLE KundenKontaktDaten
ADD CONSTRAINT MindestensEinKontakt_CHECK
CHECK (Twitter_Id IS NOT NULL OR Google_Id IS NOT NULL OR
Facebook_Id IS NOT NULL OR Skype_Id IS NOT NULL OR
Telefonnummer IS NOT NULL);
I want to avoid the multiple "OR's" and write the query in a more compact way. Is anyone aware of a way to do this?
coalesce returns the first non-null argument, or null if they are all nulls. You could utilize it in your alter table statement:
ALTER TABLE KundenKontaktDaten
ADD CONSTRAINT MindestensEinKontakt_CHECK
CHECK (COALESCE(Twitter_Id, Google_Id, Facebook_Id, Skype_Id, Telefonnummer) IS NOT NULL);
Related
I have a column 'name' in student table. I need to add NOT NULL constraint on this column. But I get SQL error saying cannot add null constraint since the existing rows in the table has null values in the column. How would I add a null constraint along with default value in a single alter statement. Below is my query.
alter table Student alter column name nvarchar NOT NULL;
SQL Server does not make this easy. I think the only way is to set the existing values to the default that you want. Then change the column to have a default value and not null:
-- Get rid of the existing `NULL` values
update students set name = '' where name is null;
-- Add the NOT NULL constraint
alter table students
alter column name varchar(255) not null;
-- Add a default value
alter table students
add constraint df_t_name default '' for name ;
Here is what it looks like in practice.
But I get SQL error saying cannot add null constraint since the existing rows in the table has null values in the column.
Have you tried overwriting the existing NULL values?
You can't have a constraint on a column when existing values would violate that constraint. You need to make your table compliant first.
I have a table viz. expenses with three columns as under
ExpenseId int NOT NULL,
ExpenseName varchar(50) NOT NULL,
Invalid bit NOT NULL
To add a new column (OldCode char(4) not null), I used design feature for tables in Microsoft SQL Server Management Studio. But I get following error
'Expenses' table
- Unable to modify table. Cannot insert the value NULL into column 'OldCode', table 'TransportSystemMaster.dbo.Tmp_Expenses'; column does not allow nulls. INSERT fails. The statement has been terminated.
Incidentally I have been able to add same column with same specifications to other tables of the same database.
Any help?
Your Table Consist of Existing Records
and you are pushing a new column of type NOT NULL.
so for older records the data have to be something.
try something like this
ALTER TABLE MY_TABLE ADD Column_name INT NULL
GO
UPDATE MY_TABLE <set valid not null values for your column>
GO
ALTER TABLE MY_TABLE ALTER COLUMN Column_name INT NOT NULL
GO
Since OldCode is NOT NULL, you should specify a default value for it.
when you have some rows on your table you can't add a column that is not nullable you should provide a default value for it
Alter Table table_name add OldCode int not null DEFAULT(0);
You have to specify values for all the 4 fields of the table, its purely because, while designing the table you set the definition of the columns to be not null. Again you are adding a new column called OldCode and setting to be not null, all ready existing records hasn't got a value. So that is the reason its complains
I want to ensure that only the values 'Expert', 'Average' or 'Adequate' are entered into the levelOfExpertise column of this table, however whenever I do try an enter one of those values, it returns an error saying the value entered is too short. Here is the create table query for this particular table. The the column I am referring to is levelOfExpertise:
CREATE TABLE MusicianInstrument
(
musicianNo varchar(5) not null
CONSTRAINT MI_PK1 REFERENCES Musician(musicianNo),
instrumentName varchar(50) not null
CONSTRAINT MI_PK2 REFERENCES Instrument(instrumentName),
levelOfExpertise varchar(50),
CONSTRAINT levelOfExpertise CHECK (levelOfExpertise = 'Expert', 'Adequate', 'Avergage'),
PRIMARY KEY(musicianNo,instrumentName)
);
Any ideas how I can ensure only those three values (Expert, Adequate or Average) can be entered?
Thanks
Use the IN operator
CHECK (levelOfExpertise IN ('Expert','Adequate','Avergage'))
Try to change your CHECK constraint as following:
CONSTRAINT levelOfExpertise CHECK (levelOfExpertise IN ('Expert','Adequate','Avergage'))
I suppose that you use sql server as RDBMS.
Can I add a column which is I specify as NOT NULL,I don't want to specify the DEFAULT value but MS-SQL 2005 says:
ALTER TABLE only allows columns to be added that can contain nulls, or have a DEFAULT definition specified, or the column being added is an identity or timestamp column, or alternatively if none of the previous conditions are satisfied the table must be empty to allow addition of this column. Column 'test' cannot be added to non-empty table 'shiplist' because it does not satisfy these conditions.
If YES, please let me know the syntax, if No please specify the reason.
No, you can't.
Because if you could, SQL wouldn't know what to put as value in the already existing records. If you didn't have any records in the table it would work without issues.
The simplest way to do this is create the column with a default and then remove the default.
ALTER TABLE dbo.MyTable ADD
MyColumn text NOT NULL CONSTRAINT DF_MyTable_MyColumn DEFAULT 'defaultValue'
ALTER TABLE dbo.MyTable
DROP CONSTRAINT DF_MyTable_MyColumn
Another alternative would be to add the column without the constraint, fill the values for all cells and add the constraint.
Add the column to the table, update the existing rows so none of them are null, and then add a "not null" constraint.
No - SQL Server quite reasonably rejects this, because it wouldn't know what value existing rows should have
It's easy to create a DEFAULT at the same time, and then immediately drop it.
I use this approach to insert NOT NULL column without default value
ALTER TABLE [Table] ADD [Column] INT NULL
GO
UPDATE [Table] SET [Column] = <default_value>
ALTER TABLE [Table] ALTER COLUMN [Column] INT NOT NULL
No.
Just use empty string '' (in case of character type) or 0 (if numeric), etc as DEFAULT value
No you cannot. But you can consider to specify the default value to ('')
No, you can't, as SQL Server, or any other database engines will force this new column to be null for existing rows into your data table. But since you do not allow a NULL, you are required to provide a default value in order to respect your own constraint. This falls under great sense! The DBE will not extrapolate a value for non-null values for the existing rows.
#Damien_The_Unbeliever's comment ,
Is it adding computed column? Neither question nor answer implied anything like that. In case of computed column the error states:
"Only UNIQUE or PRIMARY KEY constraints can be created on computed columns, while CHECK, FOREIGN KEY, and NOT NULL constraints require that computed columns be persisted"
OK, if to continue this guessing game, here is my script illustrating the adding of "NOT NULL" column in one "ALTER TABLE" step:
CREATE TABLE TestInsertComputedColumn
(
FirstName VARCHAR(100),
LastName CHAR(50)
);
insert into TestInsertComputedColumn(FirstName,LastName)
select 'v', 'gv8';
select * from TestInsertComputedColumn;
ALTER TABLE TestInsertComputedColumn
ADD FullName As FirstName + LastName PERSISTED NOT NULL;
select * from TestInsertComputedColumn;
--drop TABLE TestInsertComputedColumn;
I used below approach it worked for me
Syntax:
ALTER TABLE <YourTable> ADD <NewColumn> <NewColumnType> NOT NULL DEFAULT <DefaultValue>
Example:
ALTER TABLE Tablename ADD ColumnName datetime NOT NULL DEFAULT GETDATE();
As an option you can initially create Null-able column, then update your table column with valid not null values and finally ALTER column to set NOT NULL constraint:
ALTER TABLE MY_TABLE ADD STAGE INT NULL
GO
UPDATE MY_TABLE SET <a valid not null values for your column>
GO
ALTER TABLE MY_TABLE ALTER COLUMN STAGE INT NOT NULL
GO
I use SQL Server 2008
I use a CHECK CONSTRAINT on multiple columns in the same table to try to validate data input.
I receive an error:
Column CHECK constraint for column
'AAAA' references another column,
table 'XXXX'.
CHECK CONSTRAINT does not work in this way.
Any other way to implement this on a single table without using FK?
Thanks
Here an example of my code
CREATE TABLE dbo.Test
(
EffectiveStartDate dateTime2(2) NOT NULL,
EffectiveEndDate dateTime2(2) NOT NULL
CONSTRAINT CK_CmsSponsoredContents_EffectiveEndDate CHECK (EffectiveEndDate > EffectiveStartDate),
);
Yes, define the CHECK CONSTRAINT at the table level
CREATE TABLE foo (
bar int NOT NULL,
fred varchar(50) NOT NULL,
CONSTRAINT CK_foo_stuff CHECK (bar = 1 AND fred ='fish')
)
You are declaring it inline as a column constraint
...
fred varchar(50) NOT NULL CONSTRAINT CK_foo_fred CHECK (...)
...
Edit, easier to post than describe. Fixed your commas.
CREATE TABLE dbo.Test
(
EffectiveStartDate dateTime2(2) NOT NULL,
EffectiveEndDate dateTime2(2) NOT NULL, --need comma
CONSTRAINT CK_CmsSponsoredContents_EffectiveEndDate CHECK (EffectiveEndDate > EffectiveStartDate) --no comma
);
Of course, the question remains are you using a CHECK constraint where it should be an FK constraint...?
Check constraints can refer to a single column or to the whole record.
Use this syntax for record-level constraints:
ALTER TABLE MyTable
ADD CONSTRAINT MyCheck
CHECK (...your check expression...)
You can simply apply your validation in a trigger on the table especially that either way the operation will be rolled back if the check failed.
I found it more useful for CONSTRAINT using case statements.
ALTER TABLE dbo.ProductStock
ADD
CONSTRAINT CHK_Cost_Sales
CHECK ( CASE WHEN (IS_NOT_FOR_SALE=0 and SAL_CPU <= SAL_PRICE) THEN 1
WHEN (IS_NOT_FOR_SALE=1 ) THEN 1 ELSE 0 END =1 )