Excerpts: https://www.linuxidc.com/Linux/2012-06/62894.htm
case when The conditional then condition is true when the value of else is false and the value is end.
--Query the number of times a unified field is equal to a value.
select count(m.underwriteflag) from prpcmain m where m.underwriteflag='1' ; --720407
select count(m.nationflag) from prpcmain m where m.nationflag='1' --720422
--Merge querySelectcount(case when m.underwriteflag='1' then 1 end)Field 1, count (case when m.nationflag='1'then 1 end) field 2 from prpcmain m;
