![]() It ensures rows in one table have corresponding rows in another.A foreign key can have a different name from its primary key.In Table 2, Membership_ID is the Foreign Keyįoreign Key references the primary key of another Table! It helps connect your Tables Records can be uniquely identified in Table 1 using membership id Database – Foreign Key We have introduced a new column called Membership_id which is the primary key for table 1. Table 2 contains information on movies rented. We have divided our 1NF table into two tables viz. It is clear that we can’t move forward to make our simple database in 2 nd Normalization form unless we partition the table above. Rule 2- Single Column Primary Key that does not functionally dependant on any subset of candidate key relation.Let’s move into second normal form 2NF 2NF (Second Normal Form) Rules Hence, we require both Full Name and Address to identify a record uniquely. ![]() In our database, we have two people with the same name Robert Phil, but they live in different places. The primary key must be given a value when a new record is inserted.Ī composite key is a primary key composed of multiple columns used to identify a record uniquely.The primary key values should rarely be changed.What is a Primary Key?Ī primary is a single column value used to identify a database record uniquely. Note: Columns in a table that are NOT used to identify a record uniquely are called non-key columns. SQL Key is used to identify duplicate information, and it also helps establish a relationship between multiple tables in the database. An SQL KEY is a single column or combination of multiple columns used to uniquely identify rows or tuples in the table. The evolution of Normalization in SQL theories is illustrated below-Ī KEY in SQL is a value used to identify records in a table uniquely. However, in most practical applications, normalization achieves its best in 3 rd Normal Form. For example, there are discussions even on 6 th Normal Form. The Theory of Data Normalization in MySQL server is still being developed further. What are transitive functional dependencies?.In this Database Normalization tutorial, you will learn:
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