mysql视图错误

我有一个这样的sql查询，它给出了一个语法错误，但我找不到它是什么：

CREATE VIEW 
    vw_hs_hr_wf_main_data AS 
        select mo.wfmod_id, 
            mo.wfmod_name, 
            mo.wfmod_view_name, 
            ty.wftype_code,
            ty.wftype_description, 
            ty.wftype_table_name, 
            ty.wftype_view_name,
            ma.wfmain_id, 
            ma.wfmain_sequence,
            CASE
                WHEN ap.wf_main_app_employee IS NULL
                    THEN ma.wfmain_approving_emp_number
                ELSE ap.wf_main_app_employee
            END  CASE AS wfmain_approving_emp_number,
            ma.wfmain_flow_id,
            ty.wftype_update_field, 
            ty.wftype_assembly,
            ty.wftype_assembly_class, 
            ma.wfmain_previous_id,
            ty.wftype_cancelmain_field, 
            ma.wfmain_application_date,
            ty.wftype_cancelstatus_field, 
            ty.wftype_appmain_field,
            ty.wftype_bulk_app_flg, 
            ty.wftype_sort_field_name
        FROM hs_hr_wf_module mo INNER JOIN hs_hr_wf_type ty
            ON mo.wfmod_id = ty.wfmod_id
        INNER JOIN hs_hr_wf_main ma 
            ON ty.wftype_code = ma.wftype_code
        LEFT JOIN hs_hr_wf_main_app_person ap
            ON ma.wfmain_id = ap.wfmain_id
                AND ma.wfmain_sequence = ap.wfmain_sequence
        WHERE (ma.wfmain_iscomplete_flg = 0);

错误消息：

#1064-您的SQL语法出现错误；在第11行的"CASE AS wfmain_approving_emp_number，ma.wfmain_flow_id，ty.wftype_update_filel"附近，查看与MySQL服务器版本相对应的手册，以获得要使用的正确语法