postgresql中的SQL查询，用于生成数据透视表报告，将列转换为行

SELECT
    category,
    SUM(CASE WHEN month = 'January' THEN amount ELSE 0 END) AS january,
    SUM(CASE WHEN month = 'February' THEN amount ELSE 0 END) AS february,
    SUM(CASE WHEN month = 'March' THEN amount ELSE 0 END) AS march,
    SUM(CASE WHEN month = 'April' THEN amount ELSE 0 END) AS april,
    SUM(CASE WHEN month = 'May' THEN amount ELSE 0 END) AS may,
    SUM(CASE WHEN month = 'June' THEN amount ELSE 0 END) AS june,
    SUM(CASE WHEN month = 'July' THEN amount ELSE 0 END) AS july,
    SUM(CASE WHEN month = 'August' THEN amount ELSE 0 END) AS august,
    SUM(CASE WHEN month = 'September' THEN amount ELSE 0 END) AS september,
    SUM(CASE WHEN month = 'October' THEN amount ELSE 0 END) AS october,
    SUM(CASE WHEN month = 'November' THEN amount ELSE 0 END) AS november,
    SUM(CASE WHEN month = 'December' THEN amount ELSE 0 END) AS december
FROM
    sales
GROUP BY
    category;