How to execute this script in every schema? - mysql

Question

I have this piece of code that runs 'optimize table' to every table of a schema.
However, I need to run it to every table in every schema. How can I do that without causing problems?
set #a=null,#c=null,#b=concat("show tables where",ifnull(concat(" `Tables_in_",database(),"` like '",#c,"' and"),'')," (#a:=concat_ws(',',#a,`Tables_in_",database(),"`))");
Prepare `bd` from #b;
EXECUTE `bd`;
DEALLOCATE PREPARE `bd`;
set #a:=concat('optimize table ',#a);
PREPARE `sql` FROM #a;
EXECUTE `sql`;
DEALLOCATE PREPARE `sql`;
set #a=null,#b=null,#c=null;

Answer 1

Here is a stored procedure for your purpose.
It works by first querying INFORMATION_SCHEMA.TABLES to retrieve the list of schemas and table names. Then it goes into a loop and executes the OPTIMIZE TABLE commands sequentially.
Important note: running such a command on all tables is probably not a good idea. Specifically, you don't (or can't) adress MySQL built-in schemas. I added a WHERE clause in the query that excludes the following schemas: information_schema, performance_schema, mysql and sys. I would suggest that you further restrict the WHERE clause to your specific need (having a fixed list of schema would be a good idea).
DELIMITER $$
CREATE PROCEDURE OptimizeAllTables()
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE tableName CHAR(100);
DECLARE tableSchema CHAR(100);
DECLARE tableList CURSOR FOR
SELECT table_schema, table_name
FROM information_schema.tables
WHERE table_schema NOT IN ('information_schema', 'mysql', 'performance_schema', 'sys');
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN tableList;
tableListLoop: LOOP
SET done = FALSE;
FETCH tableList INTO tableSchema, tableName;
IF done THEN
LEAVE tableListLoop;
END IF;
SET #VarSQL = CONCAT('OPTIMIZE TABLE `', tableSchema, '`.`', tableName, '`');
-- SELECT #VarSQL;
PREPARE stmt FROM #VarSQL;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END LOOP;
CLOSE tableList;
END$$
I would also strongly suggest that you run this procedure in debug mode before executing it for real. For this, you can change this block:
-- SELECT #VarSQL;
PREPARE stmt FROM #VarSQL;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
To:
SELECT #VarSQL;
-- PREPARE stmt FROM #VarSQL;
-- EXECUTE stmt;
-- DEALLOCATE PREPARE stmt;
This will show the commands without actually executing them.
Demo on DB Fiddle (in debug mode):
-- create a few tables for testing
create table table1(id int primary key);
create table table2(id int primary key);
create table table3(id int primary key);
-- call the procedure
call OptimizeAllTables();
Yields:
| #VarSQL |
| ------------------------------ |
| OPTIMIZE TABLE `test`.`table1` |
| #VarSQL |
| ------------------------------ |
| OPTIMIZE TABLE `test`.`table2` |
| #VarSQL |
| ------------------------------ |
| OPTIMIZE TABLE `test`.`table3` |