constant usage in oracle

CONSTANT is an object that defines immutable values ​​in Oracle database. The characteristics of CONSTANT include: unmodifiable, globally visible, participating in optimization, and simplifying code. The benefits are ensuring data consistency, improving query performance, and simplifying code. Example: Create a constant pi with a value of 3.141592653589793. Use pi to query the number of records greater than pi. Note: The constant value must be legal and cannot be modified. To delete a constant, use the DROP statement.

Usage of CONSTANT in Oracle

What is CONSTANT?

CONSTANT is a constant object defined in Oracle database and is used to store immutable values.

Format of CONSTANT

<code>CREATE CONSTANT constant_name datatype [NOT NULL] AS 'constant_value';</code>

Parameters:

• constant_name: Constant name
• datatype: Constant data type
• NOT NULL: Optional, the specified constant cannot be NULL
• constant_value: Constant value

Characteristics of CONSTANT

• Constant values ​​are fixed and cannot be modified once created.
• Constants are globally visible in the database.
• Constants participate in the optimization of SQL statements.
• Constants can simplify SQL code and improve readability.

Benefits of CONSTANT

• Ensure data consistency and avoid errors.
• Improves query performance because it avoids evaluating the same expression multiple times.
• Simplify SQL code to make it easier to understand.

Example of CONSTANT

Create a constant:

<code>CREATE CONSTANT pi NUMBER AS 3.141592653589793;</code>

Use a constant:

<code>SELECT COUNT(*) FROM table_name WHERE column_name > pi;</code>

In this example, we create a constant named pi and use it in the SQL query to avoid using the exact value of π directly.

Notes

• The constant value must be a legal value of the data type.
• When creating a constant, if the NOT NULL constraint is specified, the constant value cannot be NULL.
• Modifying the constant value requires the use of the ALTER CONSTANT statement, and only the constant annotation, not the value, can be changed.
• To delete a constant, you need to use the DROP CONSTANT statement.

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