0
What else can I help you with?
What does the primary key in a data base do?
We know that primary key is the one that is not null and is always unique. A primary key uniquely identifies a record in a table.
Candidate key and primary key differnece?
All Primary keys are definitely Candidate Keys. A Candidate key is one which can be used as a Primary key that is not null and unique. That is one of the candidate keys can be chosen as a primary key.A Candidate key is a Unique Key and it can be used to find out any particular Tuple (row) in a table. The following are the differences between A Candidate key and a Primary Key: 1) A Unique key can be null but not a Primary key 2) On a table we can have only 1 primary key but 'N' number of unique keys.
How a primary key is fixed in a sql table?
A primary key field in a sql table is created using the PRIMARY KEY keyword. ex: CREATE TABLE tbl_employee ( emp_num VARCHAR(10), emp_name VARCHAR(100), PRIMARY KEY (emp_num)) The above script creates a table called tbl_employee and sets the emp_num field as the primary key
Does primary key allows null value?
No. A primary key requires a value because it is the field that all other values in the row depend on.
Is it true that a constraint is any factor that limits or restricts a design?
true because that is what it says in the glossary of my science book :)
Which constraint type enforces uniqueness?
Primary key
What is the foreign key constraint?
foreign key constraint defines a column or combinations of columns whose values match the primary key of another table.
How primary keys in database are denoted?
In the actual SQL, by means of the primary key constraint.
Features of primary key?
* In NOT NULL constraint the particular data cannot be NULL,* In UNIQUE constraint the same thing cannot be repeated, it must be unique,* The primary key is simply the combination of both these constraints.
Entity integrity constraint?
The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation. Having null value for the primary key implies that we cannot identify some tuples. This also specifies that there may not be any duplicate entries in primary key column key row.
What is key constraints?
Primary Key is a Constraint Used to avoid Duplicate entries in database table and you define primary key the column doesn't allow NULL values.
What is the difference between primary key and unique index?
Primary key is a type of unique index with no null constraint on the columns involved. There can only be one Primary key whereas you can create other unique indexes on the table.
What type of integrity is enforced when a primary key is declared?
By default a primary key is also a unique constraint, that means only one row can contain a specific value for this key (or no duplicates are allowed). Also an index is automatically created for a primary key allowing efficient access.
What is a primary key what is its purpose and why do you use it?
What is a Primary Key?The PRIMARY KEY constraint uniquely identifies each record in a database table.Primary keys must contain unique values.A primary key column cannot contain NULL values.Each table should have a primary key, and each table can have only ONE primary key.The primary key is defined by using the PRIMARY KEY constraint when either creating a table or altering a table.*Example of primary key :- customer Nowhat is its purpose and why do you use it?In relational database design, a unique key or primary key is a candidate key to uniquely identify each row in a table.
Does the primary key always consists of a single key?
No. A primary key is not null unique constraint, used to enforce uniqueness across table data. The uniqueness does not have to include a single attribute. Suppose you have a download system, which each user is allowed to download only 1 file in an hour, you will put a unique constraint on the download hour (incl. day) and the user downloading.
What is the difference between a Primary Key and a Secondary Key?
A Primary Key is a unique identifier for each record in a database table and is used to enforce entity integrity. A Secondary Key is a non-unique index that is used for querying and organizing data efficiently but does not have the constraint of uniqueness.
What rule states that either each foreign key value must match a primary key value in another relation or the foreign key value must be null?
referential integrity constraint
