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How to Use SQL Case When As

How to Use SQL Case When As

SQL is an essential part of database management and analysis. The SQL CASE WHEN statement is a powerful tool to perform conditional logic within a query. In this tutorial, you will learn how to use SQL CASE WHEN AS to transform data based on specific conditions.

Understanding SQL CASE WHEN AS

The SQL CASE WHEN statement is used to perform conditional operations in SQL. It allows you to transform data based on conditions specified in the query. SQL CASE WHEN AS is an extension of the SQL CASE WHEN statement which allows you to assign aliases to the resulting columns.

SQL CASE WHEN AS has the following syntax:

SELECT 
  column1,
  column2,
  CASE 
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ELSE default_result
  END AS alias_name
FROM table_name

In this syntax, column1 and column2 are the columns selected from the table_name. Inside the CASE statement, you can specify multiple WHEN clauses followed by a THEN clause. If none of the conditions are true, the ELSE clause specifies the default result. The AS keyword is used to assign an alias to the resulting column.

Examples

Here are some examples to help you understand how to use SQL CASE WHEN AS.

Example 1: Assigning Grades

Consider a table students that contains the following columns: id, name, score.

SELECT 
  name,
  score,
  CASE 
    WHEN score >= 90 THEN 'A'
    WHEN score >= 80 THEN 'B'
    WHEN score >= 70 THEN 'C'
    WHEN score >= 60 THEN 'D'
    ELSE 'F'
  END AS grade
FROM students

In this example, we use SQL CASE WHEN AS to assign grades based on the score. If the score is greater than or equal to 90, the grade is ‘A’. If the score is between 80 and 89, the grade is ‘B’, and so on. The resulting output will have three columns: name, score, and grade.

Example 2: Categorizing Expenses

Consider a table expenses that contains the following columns: id, category, amount.

SELECT 
  category,
  SUM(amount) AS total_amount,
  CASE 
    WHEN SUM(amount) > 1000 THEN 'High'
    WHEN SUM(amount) > 500 THEN 'Medium'
    ELSE 'Low'
  END AS expense_category
FROM expenses
GROUP BY category

In this example, we use SQL CASE WHEN AS to categorize expenses based on the total amount spent. If the total amount spent is greater than 1000, the expense category is ‘High’. If the total amount spent is between 500 and 999, the expense category is ‘Medium’, and so on. The GROUP BY clause is used to group the expenses by category, and the SUM() function is used to calculate the total amount spent in each category. The resulting output will have three columns: category, total_amount, and expense_category.

Troubleshooting Tips

  • Make sure to use the correct syntax for SQL CASE WHEN AS.
  • Double-check your conditions and results to ensure they are accurate.
  • Use aliases that are meaningful and easy to understand.

Conclusion

SQL CASE WHEN AS is a powerful tool to perform conditional operations in SQL. It allows you to transform data based on specific conditions and assign aliases to the resulting columns. By following the examples and tips in this tutorial, you can use SQL CASE WHEN AS to transform and categorize data in your own SQL queries.

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