Oracle 18c

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select * from V$VERSION;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


select 'A' as x from dual union all
select 'B'      from dual
order by x asc


X


A

B


select 'A' as x from dual union all
select 'B'      from dual union all
select 'C'      from dual union all
select 'D'      from dual union all
select 'E'      from dual
order by x asc
ORA-00904: "X": invalid identifier

select 'A' as x from dual union all
select 'B'      from dual union all
select 'C'      from dual union all
select 'D' as x from dual union all
select 'E'      from dual
order by x asc


X


A

B

C

D

E


select 'A' as x from dual union all
select 'B'      from dual union all
select 'C' as x from dual union all
select 'D'      from dual union all
select 'E'      from dual
order by x asc
ORA-00904: "X": invalid identifier

select 'A' as x from dual union all
select 'B'      from dual union all
select 'C'      from dual union all
select 'D'      from dual union all
select 'E' as x from dual
order by x asc
ORA-00904: "X": invalid identifier