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  • 表链接

    ---1. 普通的相等连接
    select e.last_name, d.department_name
    from employees e, departments d
    where e.department_id = d.department_id;
     
    ---2 左外连接 LEFT OUTER JOIN
    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);
     
    select e.last_name, d.department_name
    from employees e, departments d
    where e.department_id = d.department_id(+);
    结果为:所有员工及对应部门的记录,包括没有对应部门编号department_id的员工记录。
     

    ----3. 右外连接 right outer join
    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);
     
    select e.last_name, d.department_id,d.department_name
    from employees e, departments d
    where e.department_id(+) = d.department_id;
    结果为:所有员工及对应部门的记录,包括没有任何员工的部门记录。
     
    ----4.FULL OUTER JOIN:全外关联
    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);
    结果为:所有员工及对应部门的记录,包括没有对应部门编号department_id的员工记录和没有任何员工的部门记录。

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  • 原文地址:https://www.cnblogs.com/jeok/p/2719846.html
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