Xinxing analyzes several keywords in the database.

Xinxing analyzes several keywords in the database.

The first is the candidate keyword. It refers to the candidate keyword of a given link that has one or more attributes with unique identifiers. For example, if a student has an ID card number and a student ID number, both of them can be used as candidate keywords for the Student Entity.

Then there is the primary keyword, which is also a candidate keyword. It is selected and serves as a candidate keyword for the unique identifier of the row. A table can only have one primary key. A primary key can also be called a primary key. A primary key can be composed of one or more fields, which are called a single-field primary key and a multi-field primary key.

If a column uniquely identifies a record, we can call it a superkeyword.

If a public keyword is a primary keyword in a link, this public keyword is called an external keyword of another link. It can be seen that the external keyword represents the relationship between two links. A table that uses the external Keywords of another link as the primary keywords is called the master table, and a table with the other keywords is called the slave table of the master table. Foreign keywords are also called Foreign keys.