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mysql日期相减返回月数
1.period_diff(p1,p2) 返回在时期p1和p2之间月数(p1和p2的格式yymm或yyyymm)
例：select period_diff(date_format(g.validity,'%y%m'),date_format(now(),'%y%m')) as r from 表名 g
2.分别获取日期的year和month,总month=year*12+month
select datediff(g.validity,curdate()) as d,
g.validity,
(year(g.validity)-year(curdate()))*12 as y,
month(g.validity)-month(curdate()) as m,
(year(g.validity)-year(curdate()))*12 + month(g.validity)-month(curdate()) as result
from 表名 g
where (year(g.validity)-year(curdate()))*12 + month(g.validity)-month(curdate())
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