How to write union and order in SQL?

If you want to have Order by In your UNION Statement, then use order by in the last UNION query statement instead of the first query.

select currency from currency 
union select '-- Please Select --' as currency from currency
order by id 

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select currency from (
select currency from currency, id
union
select '-- Please Select --' as currency,0 from currency) X
order by id

select currency from currency
union select '-- Please Select --' as currency from currency
order by id

it has error:
ORDER BY items must appear in the select list if the statement contains a UNION, INTERSECT or EXCEPT operator.


select currency from (
select currency from currency, id
union
select '-- Please Select --' as currency,0 from currency) X
order by id

It has error:
Invalid object name 'id'.

id field must exists in currency table........... is it ?

select      id,
            currency
from      currency

UNION ALL

select      0,
            '-- Please Select --'
from currency
order by id

Yes, there is id field in currency table.

select      id,
            currency
from      currency

UNION ALL

select      0,
            '-- Please Select --'
from currency
order by id


It can display, but it list out 29 rows of 0, -- Please Select -- duplicated records.

And, I do not need to display id=0 on the result.

Or if you do not want to see id in the selected list, use a derived table as in:

Select      currency
From      (
      select      id
                  currency
      from      currency

      UNION ALL

      select      0,
                  '-- Please Select --'
      from currency) d

order by id

You are right:

select      id,
            currency
from      currency

UNION ALL

select      0,
            '-- Please Select --'

order by id


Or:

Select      currency
From      (
      select      id
                  currency
      from      currency

      UNION ALL

      select      0,
                  '-- Please Select --'
       ) d

order by id

Select  currency
From      (
      select      id
                  currency
      from      currency

      UNION ALL

      select      0,
                  '-- Please Select --'
      from currency) d

order by id

It has error:
All queries combined using a UNION, INTERSECT or EXCEPT operator must have an equal number of expressions in their target lists.

select      id,
            currency
from      currency

UNION ALL

select      0,
            '-- Please Select --'

order by id

It can display properly. But, how to take out the id from the result?

both excellent!