Difference Between DECODE and CASE

DECODE	CASE
DECODE is a function that compares an expression to a set of values and returns the corresponding result.	CASE is a statement that evaluates conditions and returns values based on those conditions.
DECODE(expression, search_value1, result1, search_value2, result2, ..., default_value)	CASE WHEN condition THEN result ELSE default END
DECODE is a function.	CASE is a statement.
DECODE compares an expression to a list of values, returning the result associated with the first match.	CASE allows more complex logical conditions and comparisons using WHEN and THEN.
DECODE does not handle NULL values well; it treats NULL as a special case.	CASE handles NULL values explicitly, allowing NULL conditions in WHEN clauses.
DECODE can only compare an expression to a set of values. It cannot handle complex conditions or ranges.	CASE can handle complex conditions, multiple logical tests, and ranges.
DECODE is more compact but can be less readable with multiple conditions.	CASE is more flexible and can be more readable for complex logic.
DECODE is Oracle-specific and is not part of the SQL standard.	CASE is part of the SQL standard and works across multiple database systems.
DECODE may be slightly faster for simple conditions as it is optimized for specific use cases in Oracle.	CASE is more flexible, but depending on the complexity, it might incur a slight performance overhead.

 

Examples:

DECODE Example:

SELECT employee_id,

       DECODE(department_id, 10, 'Sales', 20, 'Marketing', 'Other Department') AS department_name

FROM employees;

• In this example, DECODE checks the value of department_id:
• If department_id is 10, it returns 'Sales'.
• If department_id is 20, it returns 'Marketing'.
• Otherwise, it returns 'Other Department'.

CASE Example:

SELECT employee_id,

       CASE 

           WHEN department_id = 10 THEN 'Sales'

           WHEN department_id = 20 THEN 'Marketing'

           ELSE 'Other Department'

       END AS department_name

FROM employees;

• This CASE expression achieves the same result as the DECODE example but uses the WHEN...THEN syntax for conditions, allowing for more flexibility.

Key Differences:

1.     Syntax and Structure:

• DECODE: Requires an expression and a set of conditions in the form of expression = value. It's simpler but less flexible.
• CASE: Allows for more complex conditions and is more structured. It's standard in SQL and works across various database systems.

2.     NULL Handling:

• DECODE: Does not handle NULL values properly. If the expression or any value in the list is NULL, DECODE may behave unexpectedly.
• CASE: Explicitly handles NULL conditions, making it more robust when working with NULL values.

3.     Flexibility:

• DECODE: Suitable for simple equality conditions where you are comparing a single value to multiple possibilities.
• CASE: More flexible as it can handle complex conditions (e.g., ranges, logical comparisons like =, >, <, BETWEEN, etc.).

4.     Compatibility:

• DECODE: Oracle-specific and may not work in other database systems.
• CASE: SQL-standard, making it more portable across different databases like MySQL, PostgreSQL, SQL Server, etc.

When to Use:

• Use DECODE: When you have simple, straightforward equality checks, and you're working in an Oracle environment.
• Use CASE: When you need to handle more complex conditions, including logical comparisons or when you're working in environments that require cross-platform compatibility.