Question

My database schema looks like this:

Table t1:
    id
    valA
    valB

Table t2:
    id
    valA
    valB

What I want to do, is, for a given set of rows in one of these tables, find rows in both tables that have the same valA or valB (comparing valA with valA and valB with valB, not valA with valB). Then, I want to look for rows with the same valA or valB as the rows in the result of the previous query, and so on.

Example data:

t1 (id, valA, valB):
    1, a, B
    2, b, J
    3, d, E
    4, d, B
    5, c, G
    6, h, J

t2 (id, valA, valB):
    1, b, E
    2, d, H
    3, g, B


Example 1:

Input: Row 1 in t1
Output: 
    t1/4, t2/3
    t1/3, t2/2
    t2/1
    ...


Example 2:

Input: Row 6 in t1
Output:
    t1/2
    t2/1

I would like to have the level of the search at that the row was found in the result (e.g. in Example 1: Level 1 for t1/2 and t2/1, level 2 for t1/5, …) A limited depth of recursion is okay. Over time, I maybe want to include more tables following the same schema into the query. It would be nice if it was easy to extend the query for that purpose.

But what matters most, is the performance. Can you tell me the fastest possible way to accomplish this?

Thanks in advance!

Answer 1

try this although it’s not fully tested but looked like it was working 😛 (http://pastie.org/1140339)

drop table if exists t1;
create table t1
(
id int unsigned not null auto_increment primary key,
valA char(1) not null,
valB char(1) not null
)
engine=innodb;

drop table if exists t2;
create table t2
(
id int unsigned not null auto_increment primary key,
valA char(1) not null,
valB char(1) not null
)
engine=innodb;

drop view if exists t12;
create view t12 as
select 1 as tid, id, valA, valB from t1
union
select 2 as tid, id, valA, valB from t2;

insert into t1 (valA, valB) values 
('a','B'),
('b','J'),
('d','E'),
('d','B'),
('c','G'),
('h','J');

insert into t2 (valA, valB) values 
('b','E'),
('d','H'),
('g','B');

drop procedure if exists find_children;

delimiter #

create procedure find_children
(
in p_tid tinyint unsigned,
in p_id int unsigned 
)
proc_main:begin

declare done tinyint unsigned default 0;
declare dpth smallint unsigned default 0;


create temporary table children(
 tid tinyint unsigned not null,
 id int unsigned not null,
 valA char(1) not null,
 valB char(1) not null,
 depth smallint unsigned default 0,
 primary key (tid, id, valA, valB)
)engine = memory;

insert into children select p_tid, t.id, t.valA, t.valB, dpth from t12 t where t.tid = p_tid and t.id = p_id; 

create temporary table tmp engine=memory select * from children;

/* http://dec.mysql.com/doc/refman/5.0/en/temporary-table-problems.html */

while done <> 1 do

    if exists(
    select 1 from t12 t 
      inner join tmp on tmp.valA = t.valA or tmp.valB = t.valB and tmp.depth = dpth) then

        insert ignore into children
        select 
        t.tid, t.id, t.valA, t.valB, dpth+1 
      from t12 t
      inner join tmp on tmp.valA = t.valA or tmp.valB = t.valB and tmp.depth = dpth;

        set dpth = dpth + 1;            

        truncate table tmp;
        insert into tmp select * from children where depth = dpth;

    else
        set done = 1;
    end if;

end while;

select * from children order by depth;

drop temporary table if exists children;
drop temporary table if exists tmp;

end proc_main #


delimiter ;


call find_children(1,1);

call find_children(1,6);