一般的相等連接： select * from a, b where a.id = b.id; 這個(gè)就屬于內(nèi)連接。 對(duì)于外連接： Oracle中可以使用“(+) ”來(lái)表示，9i可以使用LEFT/RIGHT/FULL OUTER JOIN;;LEFT OUTER JOIN：左外關(guān)聯(lián);;SELECT e.last_name, e.department_id, d.department_name;;FROM employees e;;LEFT OUTER JOIN departments d;;ON (e.department_id = d.department_id);;;等價(jià)于;;SELECT e.last_name, e.department_id, d.department_name;;FROM employees e, departments d;;WHERE e.department_id=d.department_id(+);;結(jié)果為：所有員工及對(duì)應(yīng)部門的記錄，包括沒(méi)有對(duì)應(yīng)部門編號(hào)department_id的員工記錄。;;RIGHT OUTER JOIN：右外關(guān)聯(lián);;SELECT e.last_name, e.department_id, d.department_name;;FROM employees e;;RIGHT OUTER JOIN departments d;;ON (e.department_id = d.department_id);;;等價(jià)于;;SELECT e.last_name, e.department_id, d.department_name;;FROM employees e, departments d;;WHERE e.department_id(+)=d.department_id;;結(jié)果為：所有員工及對(duì)應(yīng)部門的記錄，包括沒(méi)有任何員工的部門記錄。;;FULL OUTER JOIN：全外關(guān)聯(lián);;SELECT e.last_name, e.department_id, d.department_name;;FROM employees e;;FULL OUTER JOIN departments d;;ON (e.department_id = d.department_id);;;結(jié)果為：所有員工及對(duì)應(yīng)部門的記錄，包括沒(méi)有對(duì)應(yīng)部門編號(hào)department_id的員工記錄和沒(méi)有任何員工的部門記錄。ORACLE8i是不直接支持完全外連接的語(yǔ)法，也就是說(shuō)不能在左右兩個(gè)表上同時(shí)加上(+)，下面是在ORACLE8i可以參考的完全外連接語(yǔ)法select t1.id,t2.id from table1 t1,table t2 where t1.id=t2.id(+) union select t1.id,t2.id from table1 t1,table t2 where t1.id(+)=t2.id