oracle 不支持 =和!=

-- Created on 2012/11/20 by JWW 

declare

  -- Local variables here

  i  integer := 2;

  j  integer := 2;

  k  varchar2(60);

  op varchar2(45);

begin

  -- Test statements here

  k := '';

  if (i = j and k = '') then

    --能不能输出

    op := 'k = ""有结果';

  else

    op := 'k is null有结果';

  end if;

end;

k 无论赋值还是不赋值，赋'' 或null ,都是 k is null 才生效，= ，!=无效