case when the

在SQL查询中，`CASE WHEN`是一个条件表达式，用于根据指定的条件返回不同的结果值。它通常与`THEN`和`ELSE`一起使用，形成一个简单的"如果...那么..."结构。其基本语法如下：

CASE 
   WHEN condition_1 THEN result_1
   WHEN condition_2 THEN result_2
   [ ELSE default_result ]
END

在这里，`condition_1` 和 `condition_2` 是需要评估的布尔条件，如果条件成立，对应的 `result_1` 或 `result_2` 将作为查询结果返回；如果没有匹配的条件满足，可以提供一个 `ELSE` 子句来指定默认的结果。

举个例子，假设我们有一个员工表，想根据薪水等级显示不同的信息：

SELECT 
    employee_id,
    CASE 
        WHEN salary > 5000 THEN '高级'
        WHEN salary BETWEEN 3000 AND 5000 THEN '中级'
        ELSE '初级'
    END AS salary_level
FROM employees;

这个查询将根据员工的薪水分配不同的级别。

相关问题

mysql case when

MySQL CASE WHEN statement is a conditional statement that evaluates multiple conditions and returns a value based on the first condition that is true.

The basic syntax for the MySQL case when statement is as follows:

CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
...
WHEN conditionN THEN resultN
ELSE default_result
END

Here is an example of how to use the MySQL case when statement:

SELECT first_name, last_name,
CASE
WHEN age < 18 THEN 'Minor'
WHEN age BETWEEN 18 AND 65 THEN 'Adult'
ELSE 'Senior'
END AS age_group
FROM customers;

In this example, we are selecting the first name, last name, and age group of customers from the customers table. We use the MySQL case when statement to evaluate the age of each customer and assign them to an age group based on their age. If the customer is under 18, they are assigned to the 'Minor' group, if they are between 18 and 65, they are assigned to the 'Adult' group, and if they are over 65, they are assigned to the 'Senior' group.

The resulting output would look something like this:

+------------+-----------+-----------+
| first_name | last_name | age_group |
+------------+-----------+-----------+
| John       | Doe       | Adult     |
| Jane       | Smith     | Senior    |
| Bob        | Johnson   | Minor     |
| Sarah      | Lee       | Adult     |
+------------+-----------+-----------+

tableau case when

Tableau provides the CASE WHEN statement as a conditional expression to perform logical comparisons and return different values based on those conditions. It is similar to the CASE statement in SQL.

The syntax for the CASE WHEN statement in Tableau is as follows:

CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ...
    ELSE resultN
END

Here's an example to illustrate its usage:

CASE
    WHEN [Sales] > 1000 THEN "High"
    WHEN [Sales] > 500 THEN "Medium"
    ELSE "Low"
END

In this example, if the sales value is greater than 1000, it will be labeled as "High". If it is between 500 and 1000, it will be labeled as "Medium". Otherwise, it will be labeled as "Low".

You can use the CASE WHEN statement in various scenarios, such as creating calculated fields, transforming data, or customizing visualizations based on specific conditions.