How to Alter Global Temporary Table in Oracle
In Oracle, a global temporary table (GTT) is a table that is created in the global temporary table space and is accessible by all users who have the appropriate privileges. These tables are particularly useful for storing data that is used by multiple users or applications, such as temporary lookup tables or data that needs to be shared across different sessions. However, there may be situations where you need to alter a global temporary table after it has been created. This article will guide you through the process of how to alter a global temporary table in Oracle.
Understanding Global Temporary Tables
Before diving into the alteration process, it’s important to understand the nature of global temporary tables. GTTs are session-specific, meaning that each user’s session has its own copy of the table. This session-specific copy is created when the table is first accessed by the session. When the session ends, the data in the session-specific copy is automatically dropped. The global temporary table itself, however, remains in the database.
Modifying a Global Temporary Table
To alter a global temporary table in Oracle, you can use the ALTER TABLE statement. This statement allows you to add, modify, or drop columns in the table. Here’s an example of how to alter a global temporary table:
“`sql
ALTER TABLE your_gtt_name
ADD (new_column_name column_type [CONSTRAINT constraint_name]);
“`
In this example, `your_gtt_name` is the name of your global temporary table, `new_column_name` is the name of the new column you want to add, `column_type` is the data type of the new column, and `constraint_name` (optional) is the name of the constraint you want to apply to the new column.
Adding Constraints
If you need to add constraints to an existing column or add new columns with constraints, you can do so using the ALTER TABLE statement. Here’s an example:
“`sql
ALTER TABLE your_gtt_name
ADD CONSTRAINT constraint_name CONSTRAINT_TYPE (column_name);
“`
In this example, `constraint_name` is the name of the constraint, `CONSTRAINT_TYPE` is the type of constraint (such as PRIMARY KEY, UNIQUE, or FOREIGN KEY), and `column_name` is the name of the column to which the constraint is applied.
Modifying Existing Columns
To modify an existing column, you can use the ALTER TABLE statement with the MODIFY clause. Here’s an example:
“`sql
ALTER TABLE your_gtt_name
MODIFY (column_name new_column_type);
“`
In this example, `column_name` is the name of the column you want to modify, and `new_column_type` is the new data type for the column.
Removing Columns
If you need to remove a column from a global temporary table, you can use the ALTER TABLE statement with the DROP COLUMN clause. Here’s an example:
“`sql
ALTER TABLE your_gtt_name
DROP COLUMN column_name;
“`
In this example, `column_name` is the name of the column you want to remove.
Conclusion
Altering a global temporary table in Oracle can be a straightforward process if you understand the table’s session-specific nature and the appropriate SQL statements to use. By using the ALTER TABLE statement, you can add, modify, or remove columns, as well as add constraints to your global temporary tables. Keep in mind that any changes you make to a global temporary table will affect all sessions that access the table, so make sure to communicate any changes to users and applications that rely on the table.
