Can a primary key be applied on a nullable column?

Can a primary key be applied on a nullable column?

A primary key cannot be applied on a column with a null constraint (nullable). When a table is created, by default every column is nullable. So first off all we have to remove the null constraint and apply a NOT NULL constraint on the column. To do this execute the following query. ALTER TABLE tbl_name alter column column_name int NOT NULL.

Can a null be a unique constraint in a primary key?

A unique constraint does not necessarily identify every row; it just specifies that if a row has values in its columns, then they must be unique. This is not sufficient to uniquely identify every row, which is what a primary key must do. Fundamentally speaking nothing is wrong with a NULL in a multi-column primary key.

How can I alter column to not null?

Now I want to alter it to NOT NULL and add it as primary key for that table. Since there is no other primary keys yet. I have written like below. Cannot define PRIMARY KEY constraint on nullable column in table ‘my_details’. Could not create constraint. See previous errors. How to write a single query for this?

Are there null values in Oracle primary key?

ORACLE does not permit NULL values in any of the columns that comprise a primary key. It appears that the same is true of most other “enterprise-level” systems. At the same time, most systems also allow unique contraints on nullable columns. Why is it that unique constraints can have…

How to Insert Null into primary key field?

You need to define it as an INT IDENTITY in your CREATE TABLE statement: and then when you do an INSERT, you need to explicitly specify the columns to insert, but just don’t specify the “ID” column in that list – then SQL Server will handle finding the proper value automagically:

Can a computed column be a primary key?

Don’t use computed column as a primary key, very bad idea. In your case, just define the PK on both CaseCode and ContactID columns. In the designer, select both columns, right-click and choose “set prinary key” from the menu. This appears to be a bug in the SQL Server Management Studio.

Can a primary key be a null in caseid?

Neither Case_Code nor ContactID accepts nulls, so CaseID obviously does not. When setting up CaseID I created it as NOT NULL, PRIMARY KEY, and used the formula ” [Case_Code] + CONVERT ( [varchar], [contactID], 0)”.