Este grafico permite identificar rápidamente que comando de unión entre tablas utilizar.
Select * From Tablea A Left Join Tableb B On A.Key = A.Kay
Select * From Tablea A Right Join Tableb B On A.Key = A.Kay
Select * From Tablea A Inner Join Tableb B On A.Key = A.Kay
Select * From Tablea A Left Join Tableb B On A.Key = A.Kay Where B.Key Is Null
Select * From Tablea A Left Join Tableb B On A.Key = A.Kay Where A.Key Is Null
Select * From Tablea A Full Outer Join Tableb B On A.Key = A.Kay
Select * From Tablea A Full Outer Join Tableb B On A.Key = A.Kay Where A.Key Is Null Or B.Key Is Null