sql case when 行转列

在SQL中，可以使用CASE WHEN语句实现行转列的功能。通过CASE WHEN语句，可以根据条件将一组数据显示在一行上。

下面是一个示例，演示如何使用CASE WHEN语句实现行转列：

假设有一个表格名为sales，包含以下字段：部门id（department_id）、月份（month）和收入（revenue）。

SELECT department_id,
       MAX(CASE WHEN month = 'January' THEN revenue END) AS January,
       MAX(CASE WHEN month = 'February' THEN revenue END) AS February,
       MAX(CASE WHEN month = 'March' THEN revenue END) AS March,
       MAX(CASE WHEN month = 'April' THEN revenue END) AS April,
       MAX(CASE WHEN month = 'May' THEN revenue END) AS May,
       MAX(CASE WHEN month = 'June' THEN revenue END) AS June,
       MAX(CASE WHEN month = 'July' THEN revenue END) AS July,
       MAX(CASE WHEN month = 'August' THEN revenue END) AS August,
       MAX(CASE WHEN month = 'September' THEN revenue END) AS September,
       MAX(CASE WHEN month = 'October' THEN revenue END) AS October,
       MAX(CASE WHEN month = 'November' THEN revenue END) AS November,
       MAX(CASE WHEN month = 'December' THEN revenue END) AS December
FROM sales
GROUP BY department_id;

上述查询将根据部门id将每个月的收入转换为对应的列，并将结果按部门id进行分组。