Question

I’m wondering if there is a general SQL syntax allowing for selecting unaliased numeric literals from sub-selects:

-- Seems to work in MySQL / Oracle
select table_alias."1"
from (
   select 1 from dual
) table_alias

I know I could alias the fields in the subselect:

-- Works everywhere
select table_alias.column_alias
from (
   select 1 column_alias from dual
) table_alias

But what if I don’t have control over the subselect? Also, some RDBMS allow to provide both table AND column aliases when aliasing tables:

-- Seems to work in Postgres / SQL Server
select table_alias.column_alias
from (
  select 1 from dual
) table_alias (column_alias)

But some RDBMS (e.g. MySQL) can’t do that. Is there another way?

• Note: This isn’t about any specific RDBMS, but just SQL in general
• Note: I’d like to omit the asterisk, i.e. no select *…

A related question is this one here:

Is there a generic workaround to express a derived column list in Oracle (and MySQL)?

Answer 1

According to the ANSI-92 standard it is implementation dependent. From section 7.9, 9.c:

Otherwise, the <column name> of the i-th column of the is implementation-dependent and different from the
<column name> of any column, other than itself, of a table referenced
by any <table reference> contained in the SQL-statement.

In other words, it’s all going to depend on the RDBMS that you’re using at the time.

BTW, you can check out the ANSI-92 standards if you’re looking for some fun reading.