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.
An example is determining the value of a mathematical function, using Oracle syntax:
SQL> select 4*atan(1) as "Arc tangent of 1 times 4" from dual; Arc tangent of 1 times 4 ------------------------ 3.14159265
|Firebird||SELECT expressions FROM rdb$database|
|Oracle||SELECT expressions FROM dual|