關於MySQL中查詢語句行轉列分組的問題

今天遇到乙個sql的小問題，首先需要按天查詢資料，並且需要統計每乙個不同位置的資料條數，處理的時候卡住了，特此記錄一下：

#首先，第一次寫的sql如下，先按天分組，後按指定條件分組：

select
id,date_format(created_date, '%y-%m-%d') selectday,
count_location countlocation,
count(distinct user_id) counts
from counter
where id = 32
group
by    date_format(created_date, '%y-%m-%d'),count_location
order
by    date_format(created_date, '%y-%m-%d') desc

此時需要將每天的資料合併到同一天的資料中去，實際需要的結果如下圖所示：

所以接下來實際需要處理得問題就是將多行一列轉為一行多列：

可以利用子查詢查詢出初始結果，再使用case…when…end進行合併，sql如下：

select

select1.selectday,
ifnull(case select1.countlocation when
'downpay'
then   select1.counts end,0) as
'downpay',
ifnull(case select1.countlocation   when
'villadetail'
then select1.counts end,0) as
'villadetail',
ifnull(case select1.countlocation   when
'materials'
then   select1.counts end,0) as
'materials',
ifnull(case select1.countlocation   when
'vr'
then select1.counts   end,0) as
'vr',
ifnull(case select1.countlocation   when
'godownpay'
then   select1.counts end,0) as
'godownpay'
from
(select
id,date_format(created_date, '%y-%m-%d') selectday,
count_location countlocation,
count(distinct user_id) counts
from counter
where id = 32
group
by        date_format(created_date, '%y-%m-%d'),count_location
order
by        date_format(created_date, '%y-%m-%d') desc
) select1
group
by select1.selectday,select1.countlocation
order
by select1.selectday desc

加上另乙個條件進行分組，結果如下：

可以看出每一行資料都有乙個統計好的資料，就相當於，這些資料還是分行統計了，沒有合併到同一條，這時只需要加上乙個max()函式，取每一行的最大值即可，得到最終資料，sql如下：

select

select1.selectday,
max(ifnull(case select1.countlocation when
'downpay'
then   select1.counts end,0)) as
'downpay',
max(ifnull(case select1.countlocation when
'villadetail'
then   select1.counts end,0)) as
'villadetail',
max(ifnull(case select1.countlocation when
'materials'
then select1.counts end,0)) as
'materials',
max(ifnull(case select1.countlocation when
'vr'
then select1.counts end,0)) as
'vr',
max(ifnull(case select1.countlocation when
'godownpay'
then select1.counts end,0)) as
'godownpay'
from
(select
id,date_format(created_date, '%y-%m-%d') selectday,
count_location countlocation,
count(distinct user_id) counts
from
counter
where
id = 32
group
by            date_format(created_date, '%y-%m-%d'),count_location
order
by            date_format(created_date, '%y-%m-%d') desc
) select1
group
by select1.selectday
order
by    select1.selectday desc

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