oracle中是否有isdate()等价的函数

Question

CASE WHEN ISDATE(LTRIM(RTRIM(rard.thevalue))) = 1     
THEN CONVERT(smalldatetime, LTRIM(RTRIM(rard.thevalue)))
WHEN ISDATE(LTRIM(RTRIM(rard2.thevalue))) = 1
THEN CONVERT(smalldatetime, LTRIM(RTRIM(rard2.thevalue)))
ELSE CONVERT(smalldatetime, LTRIM(RTRIM(r.receiptdate)))

I have this syntax in SQL which has to get converted into oracle. The column "thevalue" has different formats in it ex: HH:MM , MM/DD/YYYY, HH:MM:SS etc. So isdate() function is checking whether its matching the date format and then pulling the data. I would need similar kind of function to check whether the columns value is matching date time format and then display as date.

Answer 1

The Oracle equivalent would be validate_conversion() .

However, unlike SQL Server, Oracle won't recognize varying formats. You need to explicitly specify the format that you want (unless your dates already are in the format configured by nls_date_format ). Basically, you could test each possible format one after the other, and stop whenever one is recognized.

Since your purpose is to actually convert the string to a date , it would be simpler to use directly to_date() , with the on conversion error clause.

Consider something like:

coalesce(
    to_date(thevalue default null on conversion error, 'MM/DD/YYYY'),
    to_date(thevalue default null on conversion error, 'YYYY-MM-DD HH24:MI:SS'),
    ...
) 

Notes:

• the function happily ignores leading and trailing spaces, so there is no need to trim() beforehand

• this requires Oracle 12.2 or higher

• isdate() is not really safe in SQL Server; better use try_convert() , which basically behaves like Oracle's to_date() with default null on conversion error