База данных / IS_to_STUD / Soft / 2.1.0.17798-Final / Firebird-2.1.0.17798-0_Win32 / doc / sql.extensions / README.joins

-------------- New JOIN types -------------- Author: Adriano dos Santos Fernandes Format: ::= JOIN USING ( ) ::= NATURAL JOIN Notes: Named columns join: 1) All columns specified in should exist in the tables of both sides. 2) An equi-join (. = .) is automatically created for all columns (ANDed). 3) The USING columns can be accessed without qualifier, and in this case, result of it is COALESCE(., .). 4) In "SELECT *", USING columns are expanded once, using the above rule. Natural join: 1) A "named columns join" is automatically created with all columns common to the left and right tables. 2) If the is no common column, a CROSS JOIN is created. Examples: 1) select * from employee join department using (dept_no); 2) select * from employee_project natural join employee natural join project;