4

我知道如何在 SQL Server (T-SQL) 中转换为日期，但如何创建 UDF 以便每次在代码中调用它？

示例 1：下面的代码会将这个 20120428 格式化为 04/28/2012

SELECT CONVERT(CHAR(10), CONVERT(DATE, TEST_DATE), 101) AS MY_DATE
FROM
MEMBER
WHERE ISDATE(TEST_DATE) <> 0

示例 2：下面的代码会将这个 20120428 格式化为 2012-04-28

SELECT CONVERT(DATE, TEST_DATE) AS MY_DATE
FROM
MEMBER
WHERE ISDATE(TEST_DATE) <> 0

感谢您的输入！

盖伊

4

1 回答 1

6

对于第二个示例，您可以这样做：

CREATE FUNCTION dbo.ConvertDate(@d CHAR(10))
RETURNS DATE
AS
BEGIN
    RETURN (SELECT CONVERT(DATE, @d));
END
GO

但更灵活的方法可能是：

CREATE FUNCTION dbo.ConvertRegional
(
  @d CHAR(10),
  @style TINYINT
)
RETURNS CHAR(10)
AS
BEGIN
    RETURN (SELECT CONVERT(CHAR(10), CONVERT(DATE, @d), @style));
END
GO

DECLARE @d CHAR(10);
SELECT @d = '20120428';

SELECT 
 dbo.ConvertDate(@d),
 dbo.ConvertRegional(@d, 101),
 dbo.ConvertRegional(@d, 103),
 dbo.ConvertRegional(@d, 120);

结果：

----------  ----------  ----------  ----------
2012-04-28  04/28/2012  28/04/2012  2012-04-28

如果您不想继续从源表中过滤掉错误的非日期（在 WHERE 子句中保留 ISDATE() 应该可以防止函数必须处理这些行），您可以通过这种方式更改函数以避免错误，如果 NULL 可以作为替代：

CREATE FUNCTION dbo.ConvertRegional
(
  @d CHAR(10),
  @style TINYINT
)
RETURNS CHAR(10)
AS
BEGIN
    RETURN (SELECT CASE WHEN ISDATE(@d) = 1 THEN
      CONVERT(CHAR(10), CONVERT(DATE, @d), @style)
      END);
END
GO

在 SQL Server 2012 中，您可以改为执行此操作，无需编写自己的 CASE 即可执行相同的操作：

CREATE FUNCTION dbo.ConvertRegional
(
  @d CHAR(10),
  @style TINYINT
)
RETURNS CHAR(10)
AS
BEGIN
    RETURN (SELECT CONVERT(CHAR(10), TRY_CONVERT(DATE, @d), @style));
END
GO

(In fact in SQL Server 2012 you can also use FORMAT() so that you don't have to memorize the style numbers, but since I don't know what version you're using I'll leave that for another day.)

All that said, other than saving a few keystrokes in your queries, this encapsulation is actually going to make your queries perform worse (depending on where they are used). For simple conversions like this it is much better to just perform them inline in most cases.

于 2012-04-29T03:14:22.680 回答