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What is an identity column in DB2?
An identity column contains a unique numeric value for each row in the table. DB2® can automatically generate sequential numeric values for this column as rows are inserted into the table. Thus, identity columns are ideal for primary key values, such as employee numbers or product numbers.
What is generated in SQL?
The generated SQL SELECT statement has all columns from the selected table. If the table contains a large number of columns, to avoid enumerating the various column names you can choose all columns using the Generate Query with * option.
Is identity column an index?
A identity column is always a Candidate Key, but it’s artificial and you may want the natural Candidate Key as the PK. Clustered Index instead is about how the index will be created from the data and stored. There can only be one clustered index and it will be the only index that refers to the data in the table.
What is sequence in DB2?
A sequence is a stored object that simply generates a sequence of numbers in a monotonically ascending (or descending) order. A sequence provides a way to have DB2® automatically generate unique integer primary keys and to coordinate keys across multiple rows and tables.
When does the system generate value for the identity column?
The system always generates a value for the identity column. An exception is raised if the user supplies a value for the identity column. The system generates a value for the identity column only if the user does not supply a value for it.
How to create an identity column in SQL?
SQL identity column is a column whose values are automatically generated when you add a new row to the table. To define an identity column, you use the GENERATED AS IDENTITY property as follows: column_name data_type GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_option ) ] In this syntax: The data_type can be any integer data type.
What does the generated always as identity do?
The GENERATED ALWAYS generates sequential integers for the identity column. If you attempt to insert (or update) a value into the GENERATED ALWAYS AS IDENTITY column, the database system will raise an error. The GENERATED BY DEFAULT generates sequential integers for the identity column.
Is the ID column a primary key column?
The id column is of type LONG, is defined as GENERATED BY DEFAULT, and it is not a primary key column. This example also demonstrates how to specify a CYCLE and CACHE sequence generator attributes. The system will only generate a value during INSERT/UPSERT/UPDATE if the user did not supply a value.
https://www.youtube.com/watch?v=ZDcBmJNMaFs