mysql求2個或以上字段為NULL值的案例分享

核心代碼

/*--------------------------------
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 select
1,1,1,1,1,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 $$
create procedure usp_c_null()
begin 
declare n_c int;
declare idd int;
declare cur cursor for 
select id,case char_length(concat(ifnull(id1,'@'),ifnull(id2,'@'),ifnull(id3,'@'),ifnull(id4,'@'),ifnull(id5,'@'),ifnull(id6,'@')))
-char_length(replace(concat(ifnull(id1,'@'),ifnull(id2,'@'),ifnull(id3,'@'),ifnull(id4,'@'),ifnull(id5,'@'),ifnull(id6,'@')),'@','') )
 when 6 then 6 when 5 then 5 when 4 then 4  when 3 then 3 when 2 then 2 when 1 then 1 else 0 end as c from t1;
declare exit HANDLER for not found close cur ;
open cur;
repeat 
fetch cur into idd,n_c;
if(n_c>=2) then
select * from t1 where id=idd;
end if ;
until 0 end repeat;
close cur;
end ;
$$
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)
*/

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