T-SQL:将行转换为列

1. 使用PIVOT函数 使用PIVOT函数可以将行数据转换成列数据。下面是一个例子：

SELECT *
FROM (
    SELECT ProductId, Month, Revenue
    FROM Sales
) s
PIVOT (
    SUM(Revenue)
    FOR Month IN ([January], [February], [March])
) p;

2. 使用CASE WHEN语句 使用CASE WHEN语句可以将行数据转换成列数据，前提是你要知道转换后列的个数。下面是一个例子：

SELECT
    ProductId,
    SUM(CASE WHEN Month = 'January' THEN Revenue ELSE 0 END) AS January,
    SUM(CASE WHEN Month = 'February' THEN Revenue ELSE 0 END) AS February,
    SUM(CASE WHEN Month = 'March' THEN Revenue ELSE 0 END) AS March
FROM Sales
GROUP BY ProductId;