Convert date - "0713" to "July 2013"

Question

I have a table on sql server (SSMS) with a column that contains 4-digit codes. Say 0713 stands for July 2013, and 0114 stands for Jan 2014. Now I want to convert the former to the latter, I wonder what can be the most efficient sql query to convert?

Thanks for any advice!

Answer 1

Probably the most efficient way is a case statement:

select (case left(col, 2)
          when '01' then 'January '
          when '02' then 'Feburary '
          . . .
          when '12' then 'December '
        end) + right(col, 2)

This has the fewest calls to functions. There are more concise ways to do this, such as:

select datename(month, cast('2013' + col as datetime)) + right(col, 2)

Of course, to get the most efficient, you should set up a test in your environment on something like 1 million records and actually test the different timings.

For instance, it might be fastest to have a reference table with 366 entries, one for each day, and use a join to do the conversion.

Answer 2

On your final format it looks like you are wavering between values (Jan for January, but the full month name for July, instead of Jul). In that case, a look up table for the formatted months and a query to it.

Your FormattedMonth table could contain MonthName (the string you want to use) and MonthNumber (this would be most efficient as an int)

For Example:

SELECT originaldates.identifier, FormattedMonth.MonthName + ' 20' + originaldates.year
FROM (Select identifier, left(shortdate,2) as month, right(shortdate,2) as year
        from Tablecontainingfield) originaldates
JOIN FormattedMonth 
ON   cast(FormattedMonth.MonthNumber as int) = originaldates.month