SQL case when 用法
spa
主要是给变量赋值，将连续型变量离散化，主要用SQL中的CASE WHENio
实例：table
create table table_name_new as ----将时间离散化为时间段，并建立一个新表table_name_new变量
select * ,
case
when call_period >= '00' and call_period < '08' then 'period_1'
when call_period >= '08' and call_period < '11' then 'period_2'
when call_period >= '11' and call_period < '13' then 'period_3'
when call_period >= '13' and call_period < '17' then 'period_4'
when call_period >= '17' and call_period < '19' then 'period_5'
when call_period >= '19' and call_period < '24' then 'period_6'
else NULL end time_period
from table_name -- 原表select