Can primary key be foreign key Oracle?
A foreign key is a way to enforce referential integrity within your Oracle database. The foreign key in the child table will generally reference a primary key in the parent table. A foreign key can be defined in either a CREATE TABLE statement or an ALTER TABLE statement.
What is primary key and foreign key in Oracle?
A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table. 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.
How does primary key and foreign key works?
A primary key is used to ensure data in the specific column is unique. A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. Only one primary key is allowed in a table. Whereas more than one foreign key are allowed in a table.
Is foreign key can be NULL?
By default there are no constraints on the foreign key, foreign key can be null and duplicate. while creating a table / altering the table, if you add any constrain of uniqueness or not null then only it will not allow the null/ duplicate values.
What is Oracle FOREIGN KEY constraint?
A foreign key is a constraint that’s added to a table. It allows you to specify that a column in a table refers to the primary key of another table. It’s used to relate data in two tables and improve the integrity of your data. There are two ways to create a foreign key on a table in Oracle: the inline method and the out-of-line method.
What is constraint in Oracle?
Oracle constraints are defined as the rules to preserve the data integrity in the application.
What is a foreign key in SQL?
SQL – Foreign Key. A foreign key is a key used to link two tables together. This is sometimes also called as a referencing key. A Foreign Key is a column or a combination of columns whose values match a Primary Key in a different table.
What is FOREIGN KEY constraint?
Foreign Key Constraints. A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables to control the data that can be stored in the foreign key table.