[英]PostgreSQL join query issue
I am learning PostgreSQL and was practicing questions.我正在学习 PostgreSQL 并且正在练习问题。
I am stuck at this question here我在这里被困在这个问题上
My Solution does not seem to work and I am not sure why:我的解决方案似乎不起作用,我不知道为什么:
SELECT first_name, last_name, department_id, department_name
FROM employees
JOIN departments ON departments.department_id = employees.department_id;
Their solution:他们的解决方案:
SELECT first_name, last_name, department_id, department_name
FROM employees
JOIN departments USING (department_id);
I'd really appreciate the help.我真的很感激帮助。
Your solution does not work because the field names are ambiguous.您的解决方案不起作用,因为字段名称不明确。 Try prefixing like this
尝试像这样添加前缀
SELECT
employees.first_name,
employees.last_name,
departments.department_id,
departments.department_name
FROM employees
JOIN departments ON departments.department_id = employees.department_id;
The problem does not appear when you use USING
, because then there will be only a single department_id
column in the join result.使用
USING
时不会出现问题,因为那时连接结果中将只有一个department_id
列。
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