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How do you handle the NULL primary key?
Answer: No. We can’t have a Primary Key column with a NULL value. The reason for the same is very simple, primary key purpose is to uniquely identify records. If two records of a single column have a NULL value, the column values are not considered equal.
What happens if you want to store value NULL in primary key column?
A primary key must uniquely identify a record – i.e., each record can be expressed in the terms of “the record which has a key that equals X”. Since null is not equal to any value, it cannot be used as a primary key.
Can a primary key contain a NULL value?
A primary key defines the set of columns that uniquely identifies rows in a table. When you create a primary key constraint, none of the columns included in the primary key can have NULL constraints; that is, they must not permit NULL values. NULL values are not allowed.
What does it mean if a primary key field within a record is NULL?
A Null is a value you can enter in a field or use in expressions or queries to indicate missing or unknown data. In Microsoft Visual Basic, the Null keyword indicates a Null value. Some fields, such as primary key fields, cannot contain Null.
Can a null value be inserted into a primary key?
If you truly have a primary key and MySQL allows you to insert null values, then you have defeated the point of a primary key. That means you could insert multiple rows with all null values with no way of uniquely identifying each one.
Can a primary key in a relational database be null?
Primary keys in any relational database are not allowed to be NULL – it’s one of the main, fundamental characteristics of a primary key. No primary key value can be null, nor can you do anything to render the primary key null.
Can a table have more than one null value?
are not explicitly declared as NOT NULL, MySQL declares them so implicitly (and silently). A table can have only one PRIMARY KEY. The name of a PRIMARY KEY is always PRIMARY, which thus cannot be used as the name for any other kind of index.
Do you need to specify a primary key in the INSERT statement?
if you have an identity column, you don’t need to specify it in the insert statement. However, if you have a primary key that isn’t an identity column, then you do need to specify it, because otherwise it’ll try to insert a null and primary keys by default are non-nullable.