Re: Case in Order-by clause

[Daniel Gross <daniel@xxxxxxxx>]

Hi Martijn,

> Am 03.09.2024 um 14:15 schrieb Martijn van Breden <m.vanbreden@xxxxxxxxxxxxxxxxxxxxxxxxxx>:

> select REFKL, ORDAT, ORDNR
>  from TOVF
>  order by
>    case :SortCode
>      when 'A' then ' ORDAT asc '
>      when 'D' then ' ORDAT desc '
>      else ' REFKL asc '
>    end
>    limit  10;

This ORDER BY expression doesn't work - as you can only have an expression instead of a column name. So this should work:

	order by
		case :SortCode when 'A' then ORDAT end asc,
		case :SortCode when 'D' then ORDAT end desc,
		case when :SortCode not in ('A', 'D') then REFKL end asc

Lets look into it in detail, when :SortCode is set - lets assume its 'D' then the cases will evaluate into this

	order by
		null asc,
		ordat desc,
		null asc

So - as the cases, which are not true, evaluate to null, their sorting doesn't effect the result set sequence. 

With a case, you can switch between 2 or more columns to sort, but you cannot switch the ascending or descending.

HTH
Daniel