Question

我有这个代码无效。 @SomeDate is of datetime`数据类型。我只对日期部分感兴趣，比较时不需要时间：

DECLARE @year VARCHAR = datepart(year,@SomeDate)
DECLARE @FromDate DATE = CAST(@year + '-' + CAST(1 AS varchar) + '-' + CAST(1 AS varchar) AS DATETIME)
DECLARE @ToDate DATE = CAST(@year + '-' + CAST(5 AS varchar) + '-' + CAST(1 AS varchar) AS DATETIME)

IF (@SomeDate NOT BETWEEN @FromDate AND @ToDate)

分配@FromDate和@ToDate变量时失败了，它说：转换varchar到日期时间超出了间隔

尝试＃1：

DECLARE @year VARCHAR(4) = datepart(year,@SomeDate)
DECLARE @FromDate DATE = CAST(@year + '-' + CAST(1 AS varchar(2)) + '-' + CAST(1 AS varchar(2)) AS DATETIME)
DECLARE @ToDate DATE = CAST(@year + '-' + CAST(5 AS varchar(2)) + '-' + CAST(1 AS varchar(2)) AS DATETIME)

IF (@SomeDate NOT BETWEEN @FromDate AND @ToDate)

但没有工作

Answer 1

它失败了，因为您没有为任何varchars指定长度。看看@Year的结果。它将成为*（未指定长度被视为varchar（1），在这种情况下，SQL会扭曲为星号）。将@year的长度指定为varchar（4）（并在cast语句中执行相同操作）。您应该养成始终指定数据类型长度的习惯，以避免出现这类问题。

e.g。

declare @someDate datetime = getdate()

DECLARE @year VARCHAR(4) = datepart(year,@SomeDate)
DECLARE @FromDate DATE = CAST(@year + '-' + CAST(1 AS varchar(2)) + '-' + CAST(1 AS varchar(2)) AS DATETIME)
DECLARE @ToDate DATE = CAST(@year + '-' + CAST(5 AS varchar(2)) + '-' + CAST(1 AS varchar(2)) AS DATETIME)

IF (@SomeDate NOT BETWEEN @FromDate AND @ToDate)
select 1

Answer 2

您可以稍微简化一下

示例（请参阅声明@FromDate和@ToDate）

Declare @SomeDate date = GetDate()

Declare @FromDate date = DateName(YEAR,@SomeDate)+'0101'
Declare @ToDate   date = DateName(YEAR,@SomeDate)+'0501'

Select FromDate = @FromDate
      ,ToDate   = @ToDate
      ,SomeDate = @SomeDate
      ,IsBetween = case when @SomeDate between @FromDate and @ToDate then 'Yes' else 'No' end

<强>返回

FromDate    ToDate      SomeDate    IsBetween
2017-01-01  2017-05-01  2017-09-12  No

SQL Server：比较日期范围之间的日期

2 个答案: