英语口语面试mysql数据库unsigned的⽤法
1. 在mysql数据库中，unsigned表⾯含义是 '⽆符号’的意思,unsigned既为⾮负数，⽤此类型可以增加数据长度.
suck是什么意思例如，如果 int最⼤是2147683647，那 tint unsigned 最⼤ 就可以到 2147683647 * 2
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翻译官全文2. 与unsigned类似的还有binary,unsigned 属性只针对整型，⽽binary属性只⽤于char 和varchar。
3. 当设置为unsigned时候，报错BIGINT UNSIGNED value is out of range…如何解决
使⽤unsigned限制数值范围为正数的时候，如果执⾏相减操作产⽣负数；就会报错；解决⽅法
核⼼： 使⽤ cast(targetCol as signed) 将所有涉及到的unsigned字段先转化为signed类型后，再进⾏运算
-- 需要添加四个计算值计算每⽇变化数据
-- dayConfirmed: 每⽇确诊
-- dayRecovered: 每⽇康复
-- dayDeaths: 每⽇死亡
-- dayExisting: 当⽇现存
lect n.id,
2018考研政治n.deaths,
n.day_date,
berth
(firmed as signed) - firmed as signed)) as dayConfirmed,
(vered as signed) - vered as signed)) as dayRecovered,
riedel(cast(n.deaths as signed) - cast(m.deaths as signed)) as dayDeaths,
(firmed as signed) - vered as signed) - cast(n.deaths as signed)) as dayExisting
take down
from region_data_total as n
join region_data_total as m on date_sub(n.day_date, interval 1 day) = m.day_date
早间主播ion_id = m.region_id and n.day_date = (lect max(day_date) from region_data_total);加拿大硕士留学条件
