Run MySQL queries on different databases - mysql

Question

We have a system where we have for each division a database , currently we have 20+ divisions.
So when we have to update / delete / alter / new table we have to go threw all of those database and run the queries .
Sometime people don't follow procedures (always ?) and we end up having structures that aren't updated .
I was looking into a way to lunch the same queries on all database without having to use bash or external scripts .
So here is some of the stuff that i found :
CALL FOR EACH("SELECT databases WHERE `DATABASE` LIKE 'division_%'" , ${1});
where i could enter a query in the ${1}
or this (less dynamic):
call $('{a, b}' , 'ALTER TABLE division_${1}.caching ADD COLUMN notes VARCHAR(4096) CHARSET utf8'');
But this gives me "No database Selected"
Any idea on how to proceed with this situation ?

Answer 1

This is a solution i found and it works :
USE division_global;
DELIMITER $$
CREATE PROCEDURE `MultipleSchemaQuery`()
BEGIN
declare scName varchar(250);
declare q varchar(2000);
DROP TABLE IF EXISTS ResultSet;
create temporary table ResultSet (
option_value varchar(200)
);
DROP TABLE IF EXISTS MySchemaNames;
create temporary table MySchemaNames (
schemaName varchar(250)
);
insert into MySchemaNames
SELECT distinct
TABLE_SCHEMA as SchemaName
FROM
`information_schema`.`TABLES`
where
TABLE_SCHEMA LIKE 'division_%';
label1:
LOOP
set scName = (select schemaName from MySchemaNames limit 1);
// The Query
set #q = concat('TRUNCATE TABLE ', scName, '.caching');
PREPARE stmt1 FROM #q;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;
delete from MySchemaNames where schemaName = scName;
IF ((select count(*) from MySchemaNames) > 0) THEN
ITERATE label1;
END IF;
LEAVE label1;
END LOOP label1;
SELECT * FROM ResultSet;
DROP TABLE IF EXISTS MySchemaNames;
DROP TABLE IF EXISTS ResultSet;
END
$$
Inspired by this :
Querying multiple databases at once

Answer 2

You will need to use a stored procedure and some prepared statements as Simon pointed out in the comments:
cat procedure.sql
DELIMITER $$
DROP PROCEDURE IF EXISTS alter_all $$
CREATE PROCEDURE alter_all()
BEGIN
DECLARE done INT DEFAULT 0;
DECLARE _schema VARCHAR(30);
DECLARE cur CURSOR FOR select SCHEMA_NAME from information_schema.SCHEMATA where SCHEMA_NAME like 'division_%';
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done := 1;
OPEN cur;
alterLoop: LOOP
FETCH cur into _schema;
if done = 1 THEN
LEAVE alterLoop;
END IF;
SET #mystmt = concat('ALTER TABLE ', _schema, '.caching ADD COLUMN notes VARCHAR(4096)');
PREPARE stmt3 FROM #mystmt;
EXECUTE stmt3;
DEALLOCATE PREPARE stmt3;
END LOOP alterLoop;
CLOSE cur;
END $$
DELIMITER ;
With that, let's try it (using Server version: 5.5.35-0ubuntu0.12.04.2 (Ubuntu)):
> create schema division_1 default character set 'UTF8';
> create table division_1.caching (id int not null auto_increment primary key, value varchar(10));
> create schema division_2 default character set 'UTF8';
> create table division_2.caching (id int not null auto_increment primary key, value varchar(10));
> use division_1;
> source procedure.sql
> CALL alter_all();
Query OK, 0 rows affected, 1 warning (0.05 sec)
> desc caching;
+-------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| value | varchar(10) | YES | | NULL | |
| notes | varchar(4096) | YES | | NULL | |
+-------+---------------+------+-----+---------+----------------+
> desc division_2.caching
+-------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| value | varchar(10) | YES | | NULL | |
| notes | varchar(4096) | YES | | NULL | |
+-------+---------------+------+-----+---------+----------------+