sql CASE WHEN

SQL中的CASE WHEN语句是一种条件表达式，它可以根据条件返回不同的结果。它有两种形式：一种是基于值的形式，另一种是基于条件的形式。基于值的形式如下：

CASE expression
    WHEN value1 THEN result1
    WHEN value2 THEN result2
    ...
    ELSE default_result
END

基于条件的形式如下：

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

其中，expression是要比较的表达式，value1、value2等是expression可能取到的值，result1、result2等是对应的结果。condition1、condition2等是要判断的条件，result1、result2等是对应的结果。default_result是当没有匹配到任何条件时返回的默认结果。

CASE WHEN语句可以用于SELECT、WHERE、ORDER BY等语句中，可以根据需要进行灵活使用。

相关问题

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".

Sql Case When

SQL中的CASE WHEN语句是一种条件语句，用于根据条件对数据进行条件判断和结果返回。它通常与SELECT、UPDATE或DELETE等SQL语句结合使用。

CASE WHEN语句的基本语法如下：

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

其中，condition1、condition2等是判断条件，如果满足某个条件，则返回相应的结果。ELSE子句是可选的，用于当所有条件都不满足时的默认结果。

使用CASE WHEN语句时，可以根据不同的条件返回不同的结果，这在数据查询、更新和删除等操作中非常有用。以下是一些使用CASE WHEN语句的示例：

1. 查询符合条件的记录：

SELECT column1, column2,
    CASE
        WHEN condition1 THEN 'Condition 1'
        WHEN condition2 THEN 'Condition 2'
        ELSE 'Other'
    END AS result_column
FROM table_name;

2. 根据性别进行分组统计：

SELECT gender, COUNT(*) AS count,
    CASE
        WHEN gender = 'male' THEN 'Male'
        WHEN gender = 'female' THEN 'Female'
        ELSE 'Other'
    END AS gender_group
FROM users;

3. 根据销售额进行排名：

SELECT product_name, sales_amount,
    CASE
        WHEN sales_amount = MAX(sales_amount) THEN 'Top'
        ELSE 'Middle'
    END AS rank_column
FROM sales_table;

通过使用CASE WHEN语句，您可以根据特定的条件和需求来灵活地处理数据，并根据需要返回不同的结果。