mysql case when if

在MySQL中，`CASE WHEN` 和 `IF` 都是用于条件逻辑判断的语句，它们在某些场景下可以互换使用，但`CASE` 提供了更灵活的选项和更清晰的语句结构。

`CASE WHEN` 语句主要用于根据给定的条件返回一个值。其基本语法如下：

CASE
    WHEN condition THEN result_1
    WHEN condition2 THEN result_2
    [ ... ]
    ELSE default_result
END

例如，如果你想根据用户分数计算等级：

SELECT
    CASE
        WHEN score >= 90 THEN 'A'
        WHEN score >= 80 THEN 'B'
        ELSE 'C'
    END AS grade
FROM users;

`IF` 则是一个更简单的三元表达式，只支持两个条件：

IF (condition, true_result, false_result)

例如：

SELECT
    IF(score >= 80, 'Good', 'Poor') AS performance
FROM users;

相关问题

mysql case when里套if

在MySQL中，`CASE WHEN` 语句可以用于创建条件表达式，它类似于其他编程语言中的 `IF...ELSE` 结构。当你想要基于某个条件执行不同的操作时，可以使用 `CASE`。例如：

SELECT 
    CASE 
        WHEN condition THEN 'Result for true'
        ELSE 'Result for false or no condition met'
    END AS result_column
FROM table;

在这个例子中，`condition` 是你需要判断的表达式，如果这个条件成立（`TRUE`），则返回 `'Result for true'`；否则（`FALSE` 或者 `condition` 未满足），返回 `'Result for false or no condition met'`。

如果你想嵌套更多的条件检查，你可以继续在 `WHEN` 和 `ELSE` 后面添加更多的 `WHEN` 子句，直到遇到 `END` 关闭所有条件。例如：

SELECT 
    CASE 
        WHEN column1 = value1 THEN 'Result1'
        WHEN column1 = value2 THEN 'Result2'
        ELSE 'Default Result'
    END AS result_column
FROM table;

在这个结构里，如果 `column1` 等于 `value1`，结果就是 `'Result1'`；等于 `value2` 则是 `'Result2'`，否则取默认值 `'Default Result'`。

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     |
+------------+-----------+-----------+