DDL Primary key

Primary key is -

  • Uniquely identified column which is used to identify the row uniquely is known as primary key.
  • Primary key can be defined during the CREATE TABLE or ALTER TABLE.
  • Primary keys definition is optional in CREATE TABLE or ALTER TABLE.
  • Primary key is unique key and cannot contain NULL values.
  • Primary key can be only one column or more than one column.
  • The index on Primary key is called as Primary index.
  • If primary key is created on the specific table, the primary index will be automatically created by DB2.

Rules -

  • No duplicates are allowed under primary key.
  • Only one designated primary key can be available in a table.
  • Null values or junk values are not allowed under primary key.

Syntax -

PRIMARY KEY(Column1, column2…)