How can I select the first day of a month in SQL?

2018-07-03 21:02:09

I just need to select the first day of the month of a given datetime variable.

I know it's quite easy to do using this kind of code :

select CAST(CAST(YEAR(@mydate) AS VARCHAR(4)) 
+ '/' + CAST(MONTH(@mydate) AS VARCHAR(2)) + '/01' AS DATETIME)

but this is not very elegant, and probably not very fast either.

Is there a 'better way to do this ? (I'm using SQL Server 2008)

SELECT DATEADD(month, DATEDIFF(month, 0, @mydate), 0) AS StartOfMonth

除了上述所有答案之外，还有一种基于sql 2012引入的函数的方法

SELECT DATEFROMPARTS(YEAR(@mydate),MONTH(@mydate),1)

SQL Server 2008：

SELECT DATEADD(DAY,1,EOMONTH(@mydate,-1))

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