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What is a primary key in a relational database?
A primary key is a column or a set of columns in a table whose values uniquely identify a row in the table. A relational database is designed to enforce the uniqueness of primary keys by allowing only one row with a given primary key value in a table.
What is a requirement regarding primary key in a typical SQL database?
A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values. A table can have only one primary key, which may consist of single or multiple fields.
Can we define a table without primary key?
Table does not have to have primary key.
What is the importance of primary key in a database?
Using the primary key, you can easily identify and find unique rows in the database table. They allow you to update/delete only specific records by uniquely identifying them. The table’s data is sorted based on the primary key. They help you avoid inserting duplicate records in a table.
How many tables does a relational database need?
NOTE: It doesn’t matter how simple the system is, a flat-file database design (only one table) should not be employed, because it has severe limitations and inefficiencies. Your database should contain at least two tables and set relationship between them.
What’s the process of designing a relational database?
IMPORTANT: The process of designing a relational database includes making sure fields containing only one item of data, eliminating redundant data, and making sure a table contains only data directly related to the primary key.
When do primary key constraints guarantee unique data?
Because primary key constraints guarantee unique data, they are frequently defined on an identity column. When you specify a primary key constraint for a table, the Database Engine enforces data uniqueness by automatically creating a unique index for the primary key columns.
How is information stored in a relational database?
A table should not contain duplicate information, and information should not be duplicated between tables (e.g. Store each customer address and phone number once, in one table). When each piece of information is stored in only one table, you update it in one place.