Select without tablesEdit
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 commaseparated 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
Standard  ? 

DB2 

Firebird  SELECT expressions FROM rdb$database 
Ingres  SELECT expressions 
Linter  SELECT expressions 
MonetDB  SELECT expressions 
MSSQL  SELECT expressions 
MySQL 

Oracle  SELECT expressions FROM dual 
PostgreSQL 

SQLite  SELECT expressions 
Virtuoso  ? 