How can MySQL effectively achieve conditional aggregations without direct support for 'SUM IF' and 'COUNT IF'?

Elegant Solution: Overcoming the Limitations of 'SUM IF' and 'COUNT IF' in MySQL

Despite their usefulness, MySQL lacks direct support for 'SUM IF' and 'COUNT IF' functions. This limitation can often be frustrating when dealing with conditional aggregations. However, there's an elegant solution using CASE statements.

Consider the following scenario:

| id | hour | kind |
|---|---|---|
| 1 | 10 | 1 |
| 2 | 15 | 2 |
| 3 | 20 | 1 |
| 4 | 25 | 3 |

The goal is to calculate:

• The total number of records
• The total number of hours
• The count of records where 'kind' is equal to 1

Original Attempts and MySQL's Response:

The initial attempts using 'SUM( IF(...) )' or 'COUNT( IF(...) )' result in an error. MySQL does not allow mixing aggregate functions with control structures like 'IF'.

Solution Using CASE Statement:

The CASE statement provides a conditional expression to dynamically evaluate and return values. It can be used to effectively achieve the desired conditional aggregations. Here's how:

SELECT count(id), 
    SUM(hour) as totHour, 
    SUM(case when kind = 1 then 1 else 0 end) as countKindOne

This query performs the following operations:

• count(id): Counts the total number of records.
• SUM(hour): Computes the total number of hours.
• SUM(case when kind = 1 then 1 else 0 end): Uses a CASE statement to conditionally count the number of records where 'kind' is equal to 1.

Output:

| count(id) | totHour | countKindOne |
|---|---|---|
| 4 | 70 | 2 |

By utilizing the CASE statement, we can elegantly overcome the limitations of 'SUM IF' and 'COUNT IF' in MySQL, enabling efficient conditional aggregations.

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