/*--------------------------------求2個或以上字段為NULL 的記錄t1:id, id1, id2, id3, id4, id5, id6在t1 表中有個字段；其中id是主鍵；怎樣打印其中個字段或以上為NULL 的記錄id？另外，存儲過程中怎么實現按順序一條一條讀取記錄最方便？注：主鍵id 是沒有順序的，也可能是字符串的；-----------------------------------------*/drop table if exists t1;create table t1(id int,id1 int,id2 int,id3 int,id4 int,id5 int,id6 int);insert t1 select1,1,1,1,1,null,null union all select 2,null,null,null,1,2,3 union all select 3,1,2,3,4,5,6 union all select 4,1,2,3,4,5,null union all select 5,null,3,4,null,null,null ;delimiter $$create procedure usp_c_null()begin declare n_c int;declare idd int;declare cur cursor for select id,case char_length(concat(ifnull(id1,'@'),ifnull(id2,'@'),ifnull(id3,'@'),ifnull(id4,'@'),ifnull(id5,'@'),ifnull(id6,'@')))-char_length(replace(concat(ifnull(id1,'@'),ifnull(id2,'@'),ifnull(id3,'@'),ifnull(id4,'@'),ifnull(id5,'@'),ifnull(id6,'@')),'@','') ) when 6 then 6 when 5 then 5 when 4 then 4  when 3 then 3 when 2 then 2 when 1 then 1 else 0 end as c from t1;declare exit HANDLER for not found close cur ;open cur;repeat fetch cur into idd,n_c;if(n_c>=2) thenselect * from t1 where id=idd;end if ;until 0 end repeat;close cur;end ;$$delimiter ;/*+------+------+------+------+------+------+------+| id  | id1 | id2 | id3 | id4 | id5 | id6 |+------+------+------+------+------+------+------+|  1 |  1 |  1 |  1 |  1 | NULL | NULL |+------+------+------+------+------+------+------+1 row in set (0.10 sec)+------+------+------+------+------+------+------+| id  | id1 | id2 | id3 | id4 | id5 | id6 |+------+------+------+------+------+------+------+|  2 | NULL | NULL | NULL |  1 |  2 |  3 |+------+------+------+------+------+------+------+1 row in set (0.14 sec)+------+------+------+------+------+------+------+| id  | id1 | id2 | id3 | id4 | id5 | id6 |+------+------+------+------+------+------+------+|  5 | NULL |  3 |  4 | NULL | NULL | NULL |+------+------+------+------+------+------+------+1 row in set (0.17 sec)*/