Oracle SQL更新视图

Question

I have been working with this table view for a while. Research has not proven helpful. Here is what i have. I have 3 tables - Loan_01, employee_01 and tool_01

Of those 3 tables i am pulling 7 columns to view

SELECT
l.tool_desc,
t.tool_id_from_mfg,
t.tool_mfg,
e.employee_name,
l.job_desc,
l.loan_active,
l.loan_status_change_date
FROM loan_01 l
join employee_01 e ON l.employee_email=e.employee_email
join tool_01 t ON l.tool_no=t.tool_no ;

It successfully creates and runs returning data. I attempt to update with

    UPDATe TOOL_LOAN_MINE
SET loan_active = 'Inactive',
loan_status_change_date = SYSDATE
WHERE loan_status_change_date = '18-SEP-16' AND tool_out_date = '16-SEP-16'
AND loan_active = 'Active';

It returns the ORA-01779 cannot modify a column which maps to a non key-preserved table.

If i read this post correctly - https://dba.stackexchange.com/questions/127708/updating-a-view-on-multiple-joined-tables

As long as i am making a change to the multiple (Loan) table it should update. What am i doing wrong?

Thanks in advance

Answer 1

The parent tables (employee and tool) would need explicit (non-deferrable) unique constraints on the referenced columns (employee_email and tool_no respectively).

While tool_no looks like it could be the primary key, I suspect you either don't have a unique constraint on email, or it is on some function such as UPPER(email)

If you had two employees with the same email (which might be legitimate if the employee table includes ex-employees with email addresses reused), then even though only one loan record would be updated, that would affect multiple rows in the view.