小编Adr*_*los的帖子

我想从我的employees表中选择所有列+来自同一个表的另一个计算列,而无需手动键入所有列.

我考虑过这个问题:

SELECT *, salary *2 FROM employees;

但是尝试这样做我得到错误:

923. 00000 - "未找到FROM关键字"

我试图编写一个查询来列出没有任何员工的部门的ID和名称.我找到了一个有效的查询,但我不明白为什么我的方法不起作用.

除了WHERE子句中的子查询之外,两个查询都是相同的.

我的工作方法:IN ... IS NULL(编辑:它没有回报价值)

SELECT
    department_id,
    department_name
FROM
    departments
WHERE
    department_id IN ( 
        SELECT
            department_id
        FROM
            employees
        WHERE
            department_id IS NULL
    )
ORDER BY
    department_name;

WORKING方法:NOT IN ...不是NULL

SELECT
    department_id,
    department_name
FROM
    departments
WHERE
    department_id NOT IN ( --why -> IN... IS NULL is not working?
        SELECT
            department_id
        FROM
            employees
        WHERE
            department_id IS NOT NULL
    )
ORDER BY
    department_name;