DECODE()

DECODE() is Oracle’s version of a conditional IF-THEN-ELSE logic, similar to a CASE statement.
It compares an expression to multiple values and returns the matching result.

DECODE(expression, search1, result1, search2, result2, ..., default);

• expression: the value to compare.
• search: the value you're checking against.
• result: what to return if the search value matches.
• default: what to return if no match is found (optional).




SELECT emp_id,
       first_name,
       salary,
       DECODE(emp_id,
              '453', 'divya',
              '123', 'prabhu',
              '461', 'ayyappa',
              'unknown') AS REVISED_NAME
FROM sample_emp;




Explanation:

This query checks the emp_id value and returns a custom alias name using DECODE().

🔄 How it works:

• If emp_id = '453' → return 'divya'
• If emp_id = '123' → return 'prabhu'
• If emp_id = '461' → return 'ayyappa'
• Else → return 'unknown'

 Use Cases of DECODE():

• Replace codes with readable labels
• Data transformation in reports
• Simplify IF-ELSE logic in SELECT

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