日期字段为1/1/1900时显示空字符串 [英] Show empty string when date field is 1/1/1900

问题描述

我正在查询数据库：

SELECT DISTINCT 
CASE WHEN CreatedDate = '1900-01-01 00:00:00.000' THEN '' ELSE CreatedDate END AS CreatedDate
FROM LitHoldDetails

lhd.CreatedDate是一个DateTime字段，不可为空。如果字段是最小日期（1/1/1900），我想显示一个空字符串，但是我的CASE语句不起作用;当该值在数据库中时，CreatedDate在我的查询中显示1900-01-01 00：00：00.000。我正在使用SQL Server 2008 R2。我做错了什么？

lhd.CreatedDate is a DateTime field and is non-nullable. I want to display an empty string if the field is the minimum date (1/1/1900), but my CASE statement doesn't work; CreatedDate displays 1900-01-01 00:00:00.000 in my query when that value is in the database. I'm using SQL Server 2008 R2. What am I doing wrong?

推荐答案

当您使用 CASE 表达式（不是语句），您必须知道数据类型优先级。在这种情况下，您不能将 DATETIME 设置为空字符串。尝试一下：

When you use a CASE expression (not statement) you have to be aware of data type precedence. In this case you can't just set a DATETIME to an empty string. Try it:

SELECT CONVERT(DATETIME, '');

一种解决方法是将日期显示为字符串：

One workaround is to present your date as a string:

CASE WHEN CONVERT(DATE, CreatedDate) = '1900-01-01' -- to account for accidental time
  THEN ''
  ELSE CONVERT(CHAR(10), CreatedDate, 120)
    + ' ' + CONVERT(CHAR(8), CreatedDate, 108)
END 

或者你可以在演示文稿层中介绍它所属的演示文稿。

Or you could fiddle with the presentation stuff where it belongs, at the presentation tier.

这是一个例子正如您所想要的那样：

Here is an example that works exactly as you seem to want:

DECLARE @d TABLE(CreatedDate DATETIME);

INSERT @d SELECT '19000101' UNION ALL SELECT '20130321';

SELECT d = CASE WHEN CreatedDate = '19000101'
  THEN ''
  ELSE CONVERT(CHAR(10), CreatedDate, 120)
    + ' ' + CONVERT(CHAR(8), CreatedDate, 108)
END FROM @d;

结果：

d
-------------------
                    <-- empty string
2013-03-21 00:00:00

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