我們要做一張報表表格，從mysql裡取出數據，然後按等級分組，如何實現呢？
MySQL 示例 SQL:
SELECT
ftime,
sum(cost) as cost,
count(advertiser_id) as aduser_num,
sum(pv) as pv,
sum(vc) as vc,
CASE
WHEN cost>100000 THEN ‘1’
WHEN cost>50000 and cost<=100000 THEN ‘2’
WHEN cost>10000 and cost<=50000 THEN ‘3’
WHEN cost>5000 and cost<=10000 THEN ‘4’
WHEN cost>1000 and cost<=5000 THEN ‘5’
WHEN cost>100 and cost<=1000 THEN ‘6’
ELSE ‘7’ END as cost_range
from (
SELECT
ftime,
advertiser_id,
sum(real_cash+vir_cash+gift_cash+divide_cash)/100 as cost,
sum(exposure_cnt) as pv,
sum(valid_click_cnt) as vc
from etail_day
where ftime in(20140603) group by ftime,advertiser_id
) as tmp_table
group by
ftime,CASE
WHEN cost>100000 THEN ‘1’
WHEN cost>50000 and cost<=100 THEN ‘2’
WHEN cost>10000 and cost<=50000 THEN ‘3’
WHEN cost>5000 and cost<=10000 THEN ‘4’
WHEN cost>1000 and cost<=5000 THEN ‘5’
WHEN cost>100 and cost<=1000 THEN ‘6’
ELSE ‘7’ END ;
利用SQL對某個表中的數據按照某個范圍進行等級劃分，並按照劃分後的等級 group by。實現思路見上：
（1）將該表的記錄取出，如果有函數運算的話，搞個虛擬字段表示
（2）將（1）中的查詢結果構建一張臨時表，然後弄一個臨時表別名：tmp_table
（3）從臨時表中取出數據，按范圍group by
可能會遇到的問題：
MySQL Error: Every derived table must have its own alias（這句話的意思是說每個派生出來的表都必須有一個自己的別名），那可能是別名不對，檢查下臨時表別名
可能會出現null的值，這時候
◦null和任何值都不能比較
◦null只能用is null 或者is not null 來判斷，不能用=或者！=來判斷
