sql case when怎么用

SQL中的CASE WHEN语句用于根据条件执行不同的操作。它的基本语法如下：

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

你可以根据需要添加多个WHEN和ELSE子句。每个条件都会被依次检查，如果满足条件，对应的结果将被返回。

以下是一个使用CASE WHEN语句的示例：

SELECT column1,
       column2,
       CASE
            WHEN column3 = 'A' THEN 'Category 1'
            WHEN column3 = 'B' THEN 'Category 2'
            ELSE 'Other Category'
       END AS category
FROM your_table;

在上面的示例中，根据column3的值，我们将category列设置为不同的类别名称。如果column3等于'A'，则category为'Category 1'，如果column3等于'B'，则category为'Category 2'，否则category为'Other Category'。

希望这可以帮助到你！如果你有任何其他问题，请随时提问。

相关问题

sql case when使用例子

好的，以下是一个 SQL CASE WHEN 的使用例子：

SELECT 
  product_name, 
  order_date,
  CASE 
    WHEN order_amount >= 1000 THEN 'High'
    WHEN order_amount >= 500 THEN 'Medium'
    ELSE 'Low'
  END AS order_level
FROM orders;

在上面的例子中，我们使用了 SQL 的 CASE WHEN 语句来为订单添加一个“级别”列。根据订单金额的大小，我们将其分为“高”、“中”、“低”三个级别。如果订单金额大于或等于1000，则级别为“高”，如果大于或等于500，则级别为“中”，否则为“低”。

注意！以上解释完全由人类英语在Ai的翻译，如果有值得怀疑的地方建议对照原文，谢谢！

sql case when

In SQL, the `CASE WHEN` statement is used to perform conditional logic. It is used to evaluate a set of conditions and return a value based on the result of the evaluation.

The basic syntax for the `CASE WHEN` statement is as follows:

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

Here's a breakdown of what each part of the syntax does:

- `CASE` begins the `CASE WHEN` statement.
- `WHEN` specifies the condition to be evaluated.
- `THEN` specifies the value to be returned if the condition is true.
- `ELSE` specifies the value to be returned if none of the conditions are true.
- `END` ends the `CASE WHEN` statement.

Here's an example that uses `CASE WHEN` to classify products in a table based on their prices:

SELECT product_name,
       price,
       CASE
         WHEN price < 10 THEN 'Cheap'
         WHEN price >= 10 AND price < 50 THEN 'Moderate'
         WHEN price >= 50 THEN 'Expensive'
         ELSE 'Unknown'
       END AS price_category
FROM products;

In this example, the `CASE WHEN` statement evaluates the `price` column for each row in the `products` table. If the price is less than 10, it is classified as "Cheap". If the price is between 10 and 50, it is classified as "Moderate". If the price is 50 or greater, it is classified as "Expensive". If the price is not provided, it is classified as "Unknown".