sql case when后面可以跟case when吗

是的，SQL的CASE WHEN语句可以嵌套使用。你可以在CASE WHEN后面继续添加其他的CASE WHEN语句作为条件判断。这样可以实现多个条件的判断并返回相应的结果。例如，你可以使用以下语法来实现这个需求：

CASE
WHEN sex = '2' AND name = 'hello' THEN '女'
WHEN sex = '1' THEN '男'
ELSE '其他'
END

这样，当性别为2且名字为hello时，会返回"女"，当性别为1时，会返回"男"，其他情况都会返回"其他"。

相关问题

hivesql case when then后面是否可以用count

在Hive SQL中，`CASE WHEN THEN` 结构主要用于条件判断和数据转换，它本身并不直接支持对计数的操作。如果你想在查询结果中计算满足某个条件的行数，你应该在 `WHEN` 后面使用 `COUNT()` 函数，并结合其他聚合函数如 `HAVING` 或在 `SELECT` 语句中。

例如，如果你想统计某个字段基于多个条件的行数，你可以这样做：

SELECT COUNT(*) 
FROM table_name
WHERE condition1
OR
CASE WHEN condition2 THEN true ELSE false END;

这里 `COUNT(*)` 计算的是所有满足 `condition1` 或 `condition2` 的行数。如果 `condition2` 成立，则 `true` 被视为满足条件，否则 `false`。

如果你只想针对 `CASE` 语句的结果进行计数，可以在 `CASE` 后紧跟 `ELSE` 子句并赋予一个值，然后进行计数：

SELECT COUNT(
    CASE 
        WHEN condition THEN 'matched'
        ELSE 'not matched'
    END AS category
)
FROM table_name;

在这里，`category` 列会根据 `condition` 分为两组，然后计算每组的数量。

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".