如何将两个工作SELECT查询合并为一个查询？

Question

I have two queries which work independently of one another;

SELECT e.employee_id, 
       e.first_name, 
       e.last_name, 
       e.job_id, 
        e.salary, 
        e.commission_pct, e.manager_id,  
       e.department_id,  
       j.start_date,  
       j.end_date
FROM hr.employees e
LEFT OUTER JOIN hr.job_history j 
    ON e.employee_id = j.employee_id
WHERE commission_pct IS NULL

This first one recalls the information from two different tables, hr.employees and hr.job_history .

Here is the second;

SELECT e.employee_id, 
        e.last_name, 
        m.employee_id "MgrNo",  
       m.last_name "MgrName"
FROM hr.employees e 
INNER JOIN hr.employees m ON e.manager_id=m.employee_id

This is to link employee_id with manager_id to display each employee's manager surname. However, when I try to include the two together I keep getting an error telling me I have an invalid prefix. Any ideas?

Answer 1

Try:

WITH temptable AS (
SELECT e.employee_id, e.last_name, m.employee_id "MgrNo", m.last_name "MgrName"
FROM hr.employees e 
INNER JOIN hr.employees m ON 
e.manager_id=m.employee_id)
SELECT e.employee_id, e.first_name, e.last_name, e.job_id, e.salary, e.commission_pct, e.manager_id, e.department_id, j.start_date, j.end_date, t.MgrNo, t.MgrName
FROM hr.employees e
LEFT OUTER JOIN hr.job_history j ON e.employee_id = j.employee_id
LEFT JOIN temptable t ON t.employee_id = e.employee_id
WHERE commission_pct IS NULL

This uses one as a subquery then joins its key on your first query's key.

Answer 2

It would seem that you are attempting to create a query which will produce employee salary/commission history with their manager info. You can combine the queries like this:

SELECT e.employee_id, e.first_name, e.last_name, e.job_id, e.salary,
       commission_pct, e.manager_id, e.department_id, j.start_date, j.end_date, 
       m.employee_id "MgrNo", m.last_name "MgrName"
FROM hr.employees e
INNER JOIN hr.employees m ON e.manager_id=m.employee_id
LEFT OUTER JOIN hr.job_history j ON e.employee_id = j.employee_id
WHERE commission_pct IS NULL

Answer 3

"I keep getting an error telling me I have an invalid prefix."

That is a typo. We can't spot it in a version of the query you haven't posted. But basically you just need another join in the first query like this:

SELECT e.employee_id, 
       e.first_name, 
       e.last_name, 
       e.job_id, 
       e.salary,                                     
       e.commission_pct, 
       m.employee_id "MgrNo", 
       m.last_name "MgrName",
       e.department_id, 
       j.start_date, 
       j.end_date
FROM hr.employees e
LEFT OUTER JOIN hr.job_history j 
   ON e.employee_id = j.employee_id
LEFT OUTER JOIN hr.employees m
   ON m.employee_id = e.manager_id
WHERE e.commission_pct IS NULL  

I suggest using an outer join, because normally not every employee has a manager (depending on how you have implemented the hierarchy).