You can use the following syntax to create a primary key on the “customerID” column when the “customers” table is already created and you just want to alter the table: Next, in this article on Primary Key in SQL, let us see how to use the primary key on Alter Table. To apply primary key on multiple columns while creating a table, refer to the following example:ĬONSTRAINT PK_Customer PRIMARY KEY (CustomerID,CustomerName) Immerse yourself in the world of NoSQL databases with our MongoDB Course. You can use the following syntax to create a primary key on the “customerID” column while you are creating this table: To understand the various operations present on the primary key, consider the following table: Customers Table: Now that you know what are the rules of a primary key, next in this article on Primary Key in SQL, let us see the operations of the primary key. You cannot insert a new row with a pre-existing primary key.No value in the primary key column can be NULL.Each and every table can have only one primary key.All the values in the column chosen as the primary key must be unique.Now that you know what is the primary key, next in this article on Primary Key in SQL, let us understand the rules of the primary key. For Table A, a primary key can consist of single or multiple columns. Primary keys are used along with the foreign keys to refer to various tables and form referential integrities. Also, each primary key should be unique and must not contain any NULL values. Every table can have only one primary key but can have multiple candidate keys. Primary Key Constraint is a type of key through which you can uniquely identify every tuple or a record in a table. The following topics will be covered in this article: So, in this article on Primary Key in SQL, I will discuss how each record in a table can be uniquely identified when there are relational databases present. In an era where we generate 2.5 quintillion bytes of data every day, it is very important to handle data in a proper manner and identify unique records.
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