mysql怎么使用if.else.来查询

你可以试一下先输入select 'printSEQ' from 'policyexpress' where policyno='000000600326 ' into '@cnt'

再输入if '@cnt' ='' then update policyexpress set printSEQ = '212121212' where policyno = '000000600326'

end if

select name

from tb where name='li'

union all

select top 1 '没有这名字'

from tb where not exists(select 1 from tb where name='li')

两种格式，一种是时间戳，一种是日期格式

①

SELECT IF(days = 1,"是","不是") as "是否星期天" FROM (SELECT DAYOFWEEK(FROM_UNIXTIME(time,"%Y-%m-%d")) AS days FROM table) tmp

---time是时间戳 , days = 1代表星期天

--把time 和 table 替换成你数据库的 字段和表

②

SELECT IF(days = 1,"是","不是") as "是否星期天" FROM (SELECT DAYOFWEEK(date) AS days FROM table) tmp

---date是日期格式 2017-11-21 , days = 1代表星期天

--把date 和 table 替换成你数据库的 字段和表

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