假设表中至少有一行-如果没有ROLL_ID = 5001（数字）的行，并且参数s_id的值从不为0（数字零），则where子句将不选择行。如果存在ROLL_ID = 5001的行，则将选择该行，如果参数s_id为0（数字零），则将选择所有行...
只是稍微构建了一下SQL（它和以前一样）
测试1：存在ROLL_ID = 5001的行

WITH
    students AS
        (   Select 1 "ROLL_ID", 'Not 5001' "SOME_COLUMN" From dual  Union All   
            Select 5001 "ROLL_ID", 'Here I am' "SOME_COLUMN" From dual      )

Select  * 
From    students 
Where   ( ( CASE WHEN to_char(5001) = to_char(0) THEN 1
            ELSE 0 
            END = 1 )
          OR
            students.ROLL_ID IN ( 5001 ) 
        );
--  
--  R e s u l t :
--     ROLL_ID SOME_COLUMN
--  ---------- -----------
--        5001 Here I am

测试2：相同代码-使用新样本数据，其中不存在ROLL_ID = 5001的行

WITH
    students AS
        (   Select 1 "ROLL_ID", 'Not 5001' "SOME_COLUMN" From dual  Union All   
            Select 5002 "ROLL_ID", 'Here I was' "SOME_COLUMN" From dual     )¸
-- same sql returns no rows

测试3：样本数据仍然没有ROLL_ID = 5001但param s_id = 0的行

Select  * 
From    students 
Where   ( ( CASE WHEN to_char(0) = to_char(0) THEN 1
            ELSE 0 
            END = 1 )
          OR
            students.ROLL_ID IN ( 5001 ) 
        );
--  
--  R e s u l t :
--     ROLL_ID SOME_COLUMN
--  ---------- -----------
--           1 Not 5001    
--        5002 Here I was

测试3将选择所有行-始终