sql - db2 query for multiple cases

Sql - db2 query for multiple cases

Creating a query in DB2 with multiple CASE statements can help handle complex conditional logic within your SELECT statement. Here's a basic structure on how to use multiple CASE statements in a DB2 SQL query:

SELECT column1, column2, CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 ELSE default_result1 END AS alias1, CASE WHEN condition3 THEN result3 WHEN condition4 THEN result4 ELSE default_result2 END AS alias2 FROM table_name WHERE some_condition;

Example Query

Suppose you have a table employees with columns employee_id, first_name, last_name, department, and salary. You want to create a query that classifies employees into different salary bands and also categorizes them based on their department.

Here's how you might write this query using multiple CASE statements:

SELECT employee_id, first_name, last_name, department, salary, CASE WHEN salary < 30000 THEN 'Low' WHEN salary BETWEEN 30000 AND 60000 THEN 'Medium' WHEN salary > 60000 THEN 'High' ELSE 'Unknown' END AS salary_band, CASE WHEN department = 'HR' THEN 'Human Resources' WHEN department = 'IT' THEN 'Information Technology' WHEN department = 'FIN' THEN 'Finance' ELSE 'Other' END AS department_name FROM employees WHERE salary IS NOT NULL ORDER BY salary DESC;

Explanation

  1. First CASE Statement (salary_band):
    • Classifies employees into salary bands: 'Low', 'Medium', 'High', or 'Unknown'.
  2. Second CASE Statement (department_name):
    • Converts department codes into full department names: 'Human Resources', 'Information Technology', 'Finance', or 'Other'.
  3. FROM Clause:
    • Specifies the table employees.
  4. WHERE Clause:
    • Ensures that only rows with a non-null salary are considered.
  5. ORDER BY Clause:
    • Orders the results by salary in descending order.

Tips for Using CASE Statements

  • Each CASE must end with an END.
  • Multiple CASE statements can be used in a single SELECT statement.
  • The ELSE part is optional, but it's good practice to include it to handle unexpected values.
  • Ensure that each WHEN clause covers all possible conditions to avoid unintended results.

Examples

  1. SQL DB2 query with multiple CASE statements

    Description: Use CASE statements in a DB2 query to handle multiple conditions and return different values based on each condition.

    SELECT column1, CASE WHEN condition1 THEN 'Case 1 result' WHEN condition2 THEN 'Case 2 result' ELSE 'Default result' END AS result FROM your_table;

    Replace column1, condition1, condition2, your_table, and adjust the CASE logic and result values according to your specific requirements.

  2. SQL DB2 query with CASE WHEN and ELSE

    Description: Implement a DB2 query that uses CASE WHEN to evaluate multiple conditions and return different results using ELSE for default handling.

    SELECT column1, CASE WHEN condition1 THEN 'Result 1' WHEN condition2 THEN 'Result 2' ELSE 'Default result' END AS result FROM your_table;

    Adjust column1, condition1, condition2, your_table, and the CASE logic and result values based on your actual data and conditions.

  3. SQL DB2 query with multiple CASE conditions

    Description: Write a DB2 query that uses multiple CASE conditions to evaluate different scenarios and return corresponding values.

    SELECT column1, CASE WHEN condition1 THEN 'Result 1' WHEN condition2 THEN 'Result 2' WHEN condition3 THEN 'Result 3' ELSE 'Default result' END AS result FROM your_table;

    Modify column1, condition1, condition2, condition3, your_table, and adjust the CASE logic and result values as per your specific use case.

  4. SQL DB2 query with CASE expressions

    Description: Utilize CASE expressions in a DB2 query to perform conditional evaluations and return results based on those conditions.

    SELECT column1, CASE WHEN condition1 THEN 'Result 1' WHEN condition2 THEN 'Result 2' ELSE 'Default result' END AS result FROM your_table;

    Replace column1, condition1, condition2, your_table, and adjust the CASE logic and result values according to your specific needs.

  5. SQL DB2 query with CASE statement and aggregation

    Description: Combine a CASE statement with aggregation functions in a DB2 query to summarize data based on multiple conditions.

    SELECT category, COUNT(*) AS count, SUM(CASE WHEN condition1 THEN 1 ELSE 0 END) AS condition1_count, SUM(CASE WHEN condition2 THEN 1 ELSE 0 END) AS condition2_count FROM your_table GROUP BY category;

    Replace category, condition1, condition2, and your_table, adjusting the CASE logic and aggregation functions (COUNT, SUM, etc.) as per your data analysis requirements.

  6. SQL DB2 query with nested CASE statements

    Description: Implement nested CASE statements in a DB2 query to handle complex conditional logic and return different results based on multiple conditions.

    SELECT column1, CASE WHEN condition1 THEN CASE WHEN nested_condition1 THEN 'Nested result 1' ELSE 'Nested default result' END WHEN condition2 THEN 'Result 2' ELSE 'Default result' END AS result FROM your_table;

    Modify column1, condition1, nested_condition1, condition2, your_table, and adjust the nested CASE logic and result values as needed.

  7. SQL DB2 query with CASE statement for filtering

    Description: Use a CASE statement in a DB2 query to filter rows based on multiple conditions.

    SELECT * FROM your_table WHERE CASE WHEN condition1 THEN 1 WHEN condition2 THEN 1 ELSE 0 END = 1;

    Replace condition1, condition2, and your_table with appropriate values. Adjust the CASE logic to fit your filtering criteria.

  8. SQL DB2 query with CASE and JOIN

    Description: Combine a CASE statement with JOIN operations in a DB2 query to perform conditional joins based on multiple scenarios.

    SELECT t1.column1, t2.column2, CASE WHEN condition1 THEN 'Result 1' WHEN condition2 THEN 'Result 2' ELSE 'Default result' END AS result FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id;

    Replace column1, column2, condition1, condition2, table1, table2, and adjust the JOIN conditions and CASE logic according to your specific database schema and business logic.

  9. SQL DB2 query with CASE statement for sorting

    Description: Utilize a CASE statement in a DB2 query to sort query results based on multiple conditions.

    SELECT * FROM your_table ORDER BY CASE WHEN condition1 THEN column1 WHEN condition2 THEN column2 ELSE column3 END ASC;

    Replace condition1, condition2, column1, column2, column3, and your_table with actual values. Adjust the CASE logic and sorting order (ASC or DESC) to match your requirements.

  10. SQL DB2 query with CASE and subquery

    Description: Use a CASE statement with a subquery in a DB2 query to perform conditional evaluations and retrieve results based on those conditions.

    SELECT column1, (CASE WHEN EXISTS (SELECT 1 FROM another_table WHERE condition) THEN 'Exists' ELSE 'Not Exists' END) AS result FROM your_table;

    Replace column1, another_table, condition, your_table, and adjust the CASE logic and subquery as per your specific use case.

More Tags

vscode-tasks react-server tethering polling pass-by-reference settimeout process-elevation apiconnect sbt remote-desktop

More Programming Questions

More Fitness-Health Calculators

More Statistics Calculators

More Fitness Calculators

More Electronics Circuits Calculators