SQL Dialects Reference/Select queries/Select without tables
Select without tables
Sometimes one needs to execute SQL scalar expressions without table context, i.e. make a query that would act as normal SELECT operator, evaluate given comma-separated expressions and return a table with single row and one or multiple columns (one for every individual expression). Obviously, expressions can't reference any columns from the tables, as there are none.
|Firebird||SELECT expressions FROM rdb$database|
|Oracle||SELECT expressions FROM dual|