What is difference between foreign key and primary key?
A primary key is used to assure the value in the particular column is unique. The foreign key provides the link between the two tables.
Does a foreign key have to match a primary key?
Practically, the foreign key has nothing to do with the primary key tag of another table, if it points to a unique column (not necessarily a primary key) of another table then too, it would be a foreign key.
What is the relationship between primary key and foreign key?
A foreign key is a column or a set of columns in one table that references the primary key columns in another table. The primary key is defined as a column (or set of columns) where each value is unique and identifies a single row of the table.
What is the point of having a foreign key?
Foreign keys ensure that data stays integral, consistent and updated. While a primary key makes sure that data is unique in one column, the foreign key constraints enforce referential integrity by preventing values that aren’t found in the related table’s primary key being entered.
Can a foreign key be a primary key in the same table?
If you mean “can foreign key ‘refer’ to a primary key in the same table?”, the answer is a firm yes as some replied.
Are foreign keys unique?
Foreign keys. A foreign key is a column (or group of columns) within a table that refers to (or “relates to”) a unique value in a referenced table. Each value in the foreign key column must have a matching value in the referenced table.
What problems do foreign keys introduce?
Foreign key problems. Many database users encounter foreign key errors, often due to referential integrity problems. A foreign key might point to data that no longer exists, or the foreign key’s data type doesn’t match the primary key data type, eroding referential integrity.
Can a table have both primary key and foreign key?
A table can have only one Primary Key. A table can have any number of Foreign Keys. The primary key is unique and Not Null. A foreign key can contain duplicate values also.
Can a table have 2 foreign keys?
A table can have multiple foreign keys based on the requirement.