尝试执行以下查询:

选择date_add (date_add (last_day (current_date-interval 1天)，间隔1天)，间隔-1月)

试试下面的方法:

select trunc(to_date('23-03-2021','DD-MM-YYYY'),'MM') from dual;

试试下面的方法:

select trunc(sysdate,'MM') 
from dual;

从SQL Server 2022，您可以使用DATETRUNC

SELECT DATETRUNC(month, @mydate)

为了这种需要

----Last Day of Previous Month
SELECT DATEADD(s,-1,DATEADD(mm, DATEDIFF(m,0,GETDATE()),0))
LastDay_PreviousMonth
----Last Day of Current Month
SELECT DATEADD(s,-1,DATEADD(mm, DATEDIFF(m,0,GETDATE())+1,0))
LastDay_CurrentMonth
----Last Day of Next Month
SELECT DATEADD(s,-1,DATEADD(mm, DATEDIFF(m,0,GETDATE())+2,0))
LastDay_NextMonth

这也是可行的:

    SELECT DATEADD(DAY,(DATEPART(DAY,@mydate)-1)*(-1),@mydate) AS FirstOfMonth