How to Use Default Constraint?

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I'm a newbie. I'm trying to learn default constraints.

I have created a table as below.

SQL

CREATE TABLE PERSONS1
(
Emp_ID int CONSTRAINT Constpk PRIMARY KEY,
Emp_Name varchar(40),
Emp_City varchar(20) DEFAULT 'Bangalore'
)

However, I'm unable to insert the values using the following codes.

SQL

INSERT INTO PERSONS1
VALUES ( 21, 'John',NULL)

NULL Value is updated in City column
OR

SQL

INSERT INTO PERSONS1
VALUES ( 212, 'John','')

No values in City column

OR

SQL

INSERT INTO PERSONS1
VALUES ( 213, 'John')

I get an error message for this.

Where am I going wrong? Please help me out!

I'm using sql server r2 2008

Thanks in advance!

Posted 5-Feb-13 0:07am

Newbie271

Updated 5-Feb-13 0:10am

Abhishek Pant

v2

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**Zoltán Zörgő** · Accepted Answer · 2013-02-05T00:09:00

Solution 1

The third is almost the right one, but since if you omit a field, you have to specify which are you passing.

SQL

INSERT INTO PERSONS1(Emp_ID, Emp_Name) VALUES ( 213, 'John')

Posted 5-Feb-13 0:09am

Zoltán Zörgő

Updated 5-Feb-13 0:10am

v2

Comments

RedDk 5-Feb-13 13:04pm

Credit where credit's due ...

Zoltán Zörgő 5-Feb-13 13:45pm

Thank you.

Bala Selvanayagam · Accepted Answer · 2013-02-05T00:12:00

Solution 2

try

SQL

INSERT INTO PERSONS1 (Emp_ID,Emp_Name)
VALUES ( 21, 'John');

Default constraint will come into play when you do not input any value via insert statement.

Also, hope the column Emp_Id is not an auto number column

Posted 5-Feb-13 0:12am

Bala Selvanayagam

Pete O'Hanlon · Accepted Answer · 2013-02-05T00:12:00

The reason your first two queries fail to use the default value is because you explicitly set a value there. A default value is not used to replace a null value or empty string - it is there to put in a value when you don't supply one (this is not the same as explicitly choosing a null value).

The failure in your third example is because the INSERT expects three values and you only supply two. In cases like this, you have to set the columns you are expecting to insert into yourself like this

SQL

insert into persons1(emp_id, emp_name)
values (213, 'John')

Now, when you run that query, the database engine sees that you haven't supplied a value for Emp_City, so it will apply the default value of Bangalore.