Table of Contents
Beginning
Original: In conclusion
Paraphrased: To finish up
These rules apply to a primary keys
Referential consistency
This is the beginning
A primary key allows the user to identify any record in the database. The Database Engine automatically creates an index unique for the primary keys columns when you set a primary key constraint. This allows you to find the data quickly and efficiently. This means that you can quickly identify a student by simply their ID.
These are the rules of a primarykey. Each table can have only one primary key. It is often called the “ID”. It cannot exceed 16 columns. The key must be 900 bytes long. A primary key constraint can not cause an index to be generated that exceeds 999 non-clustered and 1 clustered. Clustered is used in the absence of a clustered index. Any column defined in a primary-key constraint must have null status. If nullability has not been specified, then all columns involved in a Primary Key Constraint must have nullability set not null. Binary ordering is required if a primary secret is defined by a CLR user-defined column type. A foreign key refers to a column or combination thereof that is used for establishing and enforcing a link between data in two different tables to control which data can be stored within the foreign key table. A link is formed between two tables if the primary keys for the respective columns are referenced by the columns of another table. This column is a foreign key in another table.
Ensuring that relationships between data in multiple tables are accurate and consistent.
Referential integrity can be described as a relational database idea that says table relationships should always be consistent. This means that all foreign key fields must agree to the primary key. Any changes in the primary key field must apply to all foreign keys. The same rule applies to foreign key updates.
Referential integrity can be broken by deleting records that contain a foreign-key value in another table. Certain relational database management programs can enforce referential security by either deleting foreign keys rows or returning an error. The data dictionary might define a referential-integrity constraint, which will decide the method.
