下面是一个包含4个表的练习:https://www.w3resource.com/sql-exercises/joins-hr/sql-joins-hr-exercise-13.php
我正在尝试理解为什么要使用:
SELECT job_title, department_name, first_name || ' ' || last_name AS `enter code here`Employee_name, start_date
FROM job_history
JOIN jobs USING (job_id)
JOIN departments USING (department_id)
JOIN employees USING (employee_id)
WHERE start_date>='1993-01-01' AND start_date<='1997-08-31';
返回正确的值,同时使用
SELECT job_title, department_name, first_name || ' ' || last_name AS Employee_name, start_date
FROM job_history
JOIN jobs USING (job_id)
JOIN employees USING (employee_id)
JOIN departments USING (department_id)
WHERE start_date>='1993-01-01' AND start_date<='1997-08-31';
不返回任何内容(只是更改了联接顺序)
https://stackoverflow.com/questions/56281832
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