Question

I’ve got a set of tables named results_%, all with the same structure.

I would like to add a index to this tables.

I can get the alter statement for each table as a row of a select query result but I don’t know how to execute this statements:

select concat( 'alter table ', test_db.table_name, ' add index `did` (`did`);' ) as statement 
from information_schema.tables test_db 
where test_db.table_name like 'results_%';

What am I missing?

The ouput (which I would like to execute instead of just have it displayed to me):

+---------------------------------------------------------+
| statement                                               |
+---------------------------------------------------------+
| alter table results_Em7777_spa add index `did` (`did`); |
| alter table results_KaEng_eng add index `did` (`did`);  |
| alter table results_Ka_spa add index `did` (`did`);     |
| alter table results_Mc_spa add index `did` (`did`);     |
| alter table results_Mo_eng add index `did` (`did`);     |
| alter table results_Pe_eng add index `did` (`did`);     |
| alter table results_SU_spa add index `did` (`did`);     |
| alter table results_Ta_spa add index `did` (`did`);     |
| alter table results_ba_eng add index `did` (`did`);     |
| alter table results_br_eng add index `did` (`did`);     |
| alter table results_ca_spa add index `did` (`did`);     |
| alter table results_ch_spa add index `did` (`did`);     |
| alter table results_da_spa add index `did` (`did`);     |
| alter table results_ga_eng add index `did` (`did`);     |
| alter table results_ge_spa add index `did` (`did`);     |
| alter table results_gk_eng add index `did` (`did`);     |
+---------------------------------------------------------+
16 rows in set (0.00 sec)

[EDIT]

I tried:

drop procedure if exists altlike; 
delimiter // 
create procedure altlike() 
begin 
   set group_concat_max_len = 65535; 
   select @altrlk:= concat( 'alter table ', test_db.table_name , ' add index `did` (`did`);' )
   from information_schema.tables test_db
   where test_db.table_name like "results_%"; 
   prepare statement from @altrlk; 
   execute statement; 
end // 
delimiter ; 
call altlike();

But still no luck: It only alters the last matched table (results_gk_eng).

Answer 1

You basically printing out lines of string out of the DB, it would not automatically execute it just because it looks like a sql statement;

What you can do is either use a programming language to execute line by line as you get the results back.

Or throw this into a stored procedure where it feed a secondary block of execution.

Example: FROM http://net.tutsplus.com/tutorials/an-introduction-to-stored-procedures/ read more about it.

DELIMITER //  

CREATE PROCEDURE `proc_CURSOR` (OUT param1 INT)  
BEGIN  
    DECLARE a, b, c INT;  
    DECLARE cur1 CURSOR FOR SELECT col1 FROM table1;  
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET b = 1;  
    OPEN cur1;  

    SET b = 0;  
    SET c = 0;  

    WHILE b = 0 DO  
        FETCH cur1 INTO a;  
        IF b = 0 THEN  
            SET c = c + a;  
    END IF;  
    END WHILE;  

    CLOSE cur1;  
    SET param1 = c;  

END //