《SQL 进阶教程》case :用一条 SQL 语句进行不同条件的统计

进行不同条件的统计是case表达式的著名用法之一

select 
name,
sum(case when sex = 1 then population else 0 end) as cnt_m,
sum(case when sex = 2 then population else 0 end) as cnt_f
from city_population_copy
group by name

实现了行转列

转载于:https://www.cnblogs.com/newlangwen/p/10565583.html