oracle中的case sql

Question

這段代碼有什麼問題？

select emp_id, emp_name 
from emp 
where case when :emp.designation_id = '008' then designation_id = '003' 

Answer 1

case是一個返回值的表達式。並且case表達以end結束。而一個case表達式返回一個有效的類型。

也許你打算：

select emp_id, emp_name 
from emp 
where designation_id = (case when :emp.designation_id = '008' then designation_id = '003' end); 

表達更簡單的方法這邏輯，而case是：

where :emp.designation_id = '008' and designation_id = '003' 

但你可能真的打算：

where (:emp.designation_id = '008' and designation_id = '003') or 
     (:emp.designation_id <> '008' and designation_id = :emp.designation_id)