20190917
isnull和MySQLd的ifnull函数,可以用if()函数替代if(条件,值1,值2) 条件为真:值1,否则值2(相当于c++里的三目运算?:) select if(column2 is null, 0, cslt.self_cancel_amount) as nwe_column from table_name;
select sum(column1 - if(column2 is null, 0, cslt.self_cancel_amount)) as nwe_column from table_name;
原文:https://www.cnblogs.com/damahuhu/p/11675575.html