Sådan finder du LEFT OUTER JOIN eller RIGHT OUTER JOIN med ORACLE JOIN (+)

Forklar venligst, hvordan du finder den højre og venstre ydre sammenføjning korrekt med et eksempel

Jeg vil prøve at vise forskellen mellem Oracle outer join-syntaks og ANSI/ISO-syntaksen .

VENSTRE YDRE JOIN -

SELECT e.last_name,
  d.department_name
FROM employees e,
  departments d
WHERE e.department_id = d.department_id(+);

SELECT e.last_name,
  d.department_name
FROM employees e
LEFT OUTER JOIN departments d
ON (e.department_id = d.department_id);

HØJRE YDRE JOIN -

SELECT e.last_name,
  d.department_name
FROM employees e,
  departments d
WHERE e.department_id(+) = d.department_id;

SELECT e.last_name,
  d.department_name
FROM employees e
RIGHT OUTER JOIN departments d
ON (e.department_id = d.department_id);

FULD YDRE JOIN -

Før den oprindelige understøttelse af hash fuld outerjoin i 11gR1, ville Oracle internt konvertere FULL OUTER JOIN på følgende måde -

SELECT e.last_name,
  d.department_name
FROM employees e,
  departments d
WHERE e.department_id = d.department_id(+)
UNION ALL
SELECT NULL,
  d.department_name
FROM departments d
WHERE NOT EXISTS
  (SELECT 1 FROM employees e WHERE e.department_id = d.department_id
  );

SELECT e.last_name,
  d.department_name
FROM employees e
FULL OUTER JOIN departments d
ON (e.department_id = d.department_id);

Tag et kig på dette.