如何将子字符串中的数字转换为 SQL 中的日期格式？

Question

How do I format this particular example to a dd-mm-yyyy format?

In table say table1, we have a string in the following format where I need to take the date value out.

AB-20092018-data1 
CD-21918-notsodata1
EF-31012017-data1
GH-31117-notsodata

Answer 1

As above your 31117 records are going to be quite hard to determine what the actual date is supposed to be.

You can do something very messy like this to get your date format out of the ones that actually have a date in it.

SELECT   cast(right(convert1, 4) + '/' + substring(convert1, 3, 2) + '/' + left(convert1, 2) as date) as LongDate1
FROM    (
    select left(substring('EF-31012017-data1',CHARINDEX('-','EF-31012017-data1') +1,len('EF-31012017-data1')),charindex('-',substring('EF-31012017-data1',CHARINDEX('-','EF-31012017-data1') +1,len('EF-31012017-data1')))-1) Convert1
) longer