-- 行转列问题
# 方法1: 1, 针对id分组; 2, 针对month求和 (使用聚合函数不计算null的特性)select       id     , sum(case `month` when 'Jan' then revenue else null end) as Jan_Revenue     , sum(case `month` when 'Feb' then revenue else null end) as Feb_Revenue     , sum(case `month` when 'Mar' then revenue else null end) as Mar_Revenue     , sum(case `month` when 'Apr' then revenue else null end) as Apr_Revenue     , sum(case `month` when 'May' then revenue else null end) as May_Revenue     , sum(case `month` when 'Jun' then revenue else null end) as Jun_Revenue     , sum(case `month` when 'Jul' then revenue else null end) as Jul_Revenue     , sum(case `month` when 'Aug' then revenue else null end) as Aug_Revenue     , sum(case `month` when 'Sep' then revenue else null end) as Sep_Revenue     , sum(case `month` when 'Oct' then revenue else null end) as Oct_Revenue     , sum(case `month` when 'Nov' then revenue else null end) as Nov_Revenue     , sum(case `month` when 'Dec' then revenue else null end) as Dec_Revenuefrom Department group by id
# 方法2: 使用if做判断select id,    sum(IF(month="Jan",revenue,null)) as Jan_Revenue,    sum(IF(month="Feb",revenue,null)) as Feb_Revenue,    sum(IF(month="Mar",revenue,null)) as Mar_Revenue,    sum(IF(month="Apr",revenue,null)) as Apr_Revenue,    sum(IF(month="May",revenue,null)) as May_Revenue,    sum(IF(month="Jun",revenue,null)) as Jun_Revenue,    sum(IF(month="Jul",revenue,null)) as Jul_Revenue,    sum(IF(month="Aug",revenue,null)) as Aug_Revenue,    sum(IF(month="Sep",revenue,null)) as Sep_Revenue,    sum(IF(month="Oct",revenue,null)) as Oct_Revenue,    sum(IF(month="Nov",revenue,null)) as Nov_Revenue,    sum(IF(month="Dec",revenue,null)) as Dec_Revenuefrom Department group by id;