CREATE TABLE abc(a int auto_increment PRIMARY KEY, b varchar(1024), c
varchar(1024))ENGINE=INNODB;
INSERT INTO abc (b,c) VALUES (repeat('b', 1024), repeat('c', 1024));
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
INSERT INTO abc (b,c) SELECT b,c FROM abc;
SELECT DATA_LENGTH, INDEX_LENGTH from information_schema.TABLES WHERE
TABLE_SCHEMA = 'test' AND TABLE_NAME = 'abc';
DATA_LENGTH	INDEX_LENGTH
#	0
ALTER TABLE abc add INDEX cc (c(800));
SELECT DATA_LENGTH, INDEX_LENGTH from information_schema.TABLES WHERE
TABLE_SCHEMA = 'test' AND TABLE_NAME = 'abc';
DATA_LENGTH	INDEX_LENGTH
#	17809408
ALTER TABLE abc add INDEX bb (b(800));
SELECT DATA_LENGTH, INDEX_LENGTH from information_schema.TABLES WHERE
TABLE_SCHEMA = 'test' AND TABLE_NAME = 'abc';
DATA_LENGTH	INDEX_LENGTH
#	35618816
DROP TABLE abc;