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Save Article Primary Key: A primary key is used to ensure that data in the specific column is unique. A column cannot have NULL values. It is either an existing table column or a column that is specifically generated by the database according to a defined sequence. Example: Refer the figure – Foreign Key: Example: Refer the figure – Figure: Let’s see the difference between Primary Key and Foreign Key:
SQL FOREIGN KEY ConstraintThe A The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table. Look at the following two tables: Persons Table
Orders Table
Notice that the "PersonID" column in the "Orders" table points to the "PersonID" column in the "Persons" table. The "PersonID" column in the "Persons" table is the The "PersonID" column in the "Orders" table is a The SQL FOREIGN KEY on CREATE TABLEThe following SQL creates a MySQL: CREATE TABLE Orders ( SQL Server / Oracle / MS Access: CREATE TABLE Orders ( To allow naming of a MySQL / SQL Server / Oracle / MS Access: CREATE TABLE Orders ( SQL FOREIGN KEY on ALTER TABLETo create a MySQL / SQL Server / Oracle / MS Access: ALTER TABLE Orders To allow naming of a MySQL / SQL Server / Oracle / MS Access: ALTER TABLE Orders DROP a FOREIGN KEY ConstraintTo drop a MySQL: ALTER TABLE Orders SQL Server / Oracle / MS Access: ALTER TABLE Orders Which refers to a field or fields in a related table that identifies the primary key in a primary table?Keys. Fields that are part of a table relationship are called keys. A key usually consists of one field, but may consist of more than one field. There are two kinds of keys: Primary key A table can have only one primary key.
Which field is the primary key field?Often, a unique identification number, such as an ID number or a serial number or code, serves as a primary key in a table. For example, you might have a Customers table where each customer has a unique customer ID number. The customer ID field is the primary key.
Which key refers to a primary key of another table?The instance of the first table's primary key in the second table is referred to as a foreign key.
Is a field or fields in a table that matches the primary key of another table?A table relationship works by matching data in key fields — often a field with the same name in both tables. In most cases, these matching fields are the primary key from one table, which provides a unique identifier for each record, and a foreign key in the other table.
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