mysql中的if、ifnull、case、case when

select if(true,"真","假") as '列1',if(false,"真","假") as '列2'
from dual;

select ifnull(null,"非null") as '列1',ifnull("非null",null) as '列2'
from dual;

select
(case project.status 
when 0 then '未交付'
when 1 then '滚动交付'
when 2 then '已交付'
END
) as 状态
from project;

select
(case 
when p.STATUS = '0' then '未交付'
when p.STATUS = '1' then '滚动交付'
when p.STATUS = '2' then '已交付'
end
) as 状态
from tb_mdm_project p;

select
ifnull(p.version,0)
from tb_mdm_project p;

select
if(p.version is null,0,p.version)
from tb_mdm_project p ;

select
(case 
when p.version is null then 0
else p.version
end ) as version 
from tb_mdm_project p ;