sql的case when用法

select t.C_OPERATE_TIME MODIFY_TIME,
       t.c_code EMPLOYEE_CODE,
       t.c_name EMPLOYEE_NAME,
       CASE t.c_employee_status
         WHEN '在职' THEN
          1
         WHEN '实习生' THEN
          1
         ELSE
          0
       END BL_FLAG,
       t.c_labor_date CREATE_TIME,
       CASE t.c_ctf_type
         WHEN '身份证' THEN
          '01'
         WHEN '护照' THEN
          '08'
         ELSE
          '99'
       END USERCARDTYPE,
       t.c_personal_id USERCARDID,
       t1.c_name TITLE,
       t2.c_code ORG_CODE,
       t3.c_mobile_tel PHONE,
       t3.c_office_tel TELEPHONE,
       1 BL_SEND_GAIN,
       1 BL_DISPATCH_GAIN,
       'hcmSync' CREATE_USER_CODE,
       'hcmSync' MODIFY_USER_CODE,
       0 DEL_FLAG,
       '双重身份' EMPLOYEE_TYPE,
       'ZS_ZY' EMPLOYEE_SOURCE
  from T_BASE_STA_EMP t
  left join T_BASE_ORG_POSITION t1
    on t.c_position_hid = t1.c_oid
  left join T_BASE_ORG_ORGUNIT t2
    on t.c_dept_hid = t2.c_hid
  left join t_base_sta_attached t3
    on t.c_oid = t3.c_oid
 where t.c_operate_time >
       to_date('2018-07-18 00:00:00', 'yyyy-MM-dd hh24:mi:ss')