状况一: select (case when trim(' ') is not null then 'not null' else 'is null' end) as age from dual; 输出结果：age： 'is null' 状况二:删除trim() select (case when ' ' is not null then 'is null' else 'not null' end) as age from dual; 输出结果：age： 'not null' 由以上测试能够得出从此的判断条件为: if (trim(nvl(var_name_str,''))='') then begin your operation; end; end if; nvl用法：nvl（arg,value）表明若是前面的arg的值为null那么返回的值为后面的value