How can I substitute a left join in SQL

Question

Can anyone tell me how can I write the equivalent of a left join without really using left joins.

Select * from a left join b on a.name = b.name.
         


        

Answer 1

Oracle disguised left join:

SELECT * FROM A, B
 WHERE a.name = b.name(+)

Generic :

SELECT a.*, case c.existence WHEN 1 then c.name ELSE NULL END
  FROM A
 INNER JOIN ( SELECT name name, 1 existence FROM B
               UNION ALL
              SELECT a.name name, 0 existence FROM A
               WHERE a.name NOT IN ( SELECT name FROM B )
            ) C
    ON c.name = a.name