Not in Optimization

Select * from EMP where emp_no not in (select emp_no from emp_bill)

Because the not in efficiency is relatively low, there are two methods to optimize it:

Method 1:

Select * from emp a where not exists (select 1 from emp_bill B where B. EMP. No = A. emp_no)Select 1 is a usage. You can also select a field or select 'x'. That is to say, exists actually checks whether data is returned and does not care about the returned data.

Method 2:

Select a. * from emp a, emp_bill B where a. emp_no = B. emp_no (+) and B. emp_no is n <br/>