SELECT FORMAT(SUM(data_length+index_length)/POWER(1024,3),2) InnoDB_DiskSpace
FROM information_schema.tables
WHERE engine='InnoDB';

SELECT
    IFNULL(tbl,'Total') table_name,
    FORMAT(SUM(table_bytes)/POWER(1024,3),2) table_size
FROM
(
    SELECT table_name tbl,SUM(data_length+index_length)table_bytes
    FROM information_schema.tables WHERE table_schema='mydb
    GROUP BY table_name WITH ROLLUP
) A ORDER BY ISNULL(tbl) DESC,table_bytes;

SELECT FORMAT(SUM(data_length+index_length)/POWER(1024,3),2) Table_Diskspace
FROM information_schema.tables
WHERE table_schema='mydb;
AND table_name='mytable';

use mydb
CREATE TABLE mytable_new LIKE mytable;
INSERT INTO mytable_new SELECT * FROM mytable;
ANALYZE TABLE mytable_new;
SELECT FORMAT(SUM(data_length+index_length)/POWER(1024,3),2) Table_Diskspace
FROM information_schema.tables
WHERE table_schema='mydb;
AND table_name='mytable_new';
#
# Stop Here. If you are happy with the size, do the last two commands
# If you prefer, drop table mytable_new and do do the online schema change
#
RENAME TABLE mytable TO mytable_old,mytable_newTO mytable;
DROP TABLE mytable_old;