--eval create table t1(a int not null, b int, c char(10), d varchar(20), primary key (a)) engine = innodb default charset=$charset insert into t1 values (1,1,'ab','ab'),(2,2,'ac','ac'),(3,2,'ad','ad'),(4,4,'afe','afe'); commit; --error ER_DUP_ENTRY alter table t1 add unique index (b); insert into t1 values(8,9,'fff','fff'); select * from t1; show create table t1; alter table t1 add index (b); insert into t1 values(10,10,'kkk','iii'); -- disable_query_log -- disable_result_log analyze table t1; -- enable_result_log -- enable_query_log select * from t1; select * from t1 force index(b) order by b; explain select * from t1 force index(b) order by b; show create table t1; alter table t1 add unique index (c), add index (d); insert into t1 values(11,11,'aaa','mmm'); -- disable_query_log -- disable_result_log analyze table t1; -- enable_result_log -- enable_query_log select * from t1; select * from t1 force index(b) order by b; select * from t1 force index(c) order by c; select * from t1 force index(d) order by d; explain select * from t1 force index(b) order by b; explain select * from t1 force index(c) order by c; explain select * from t1 force index(d) order by d; show create table t1; check table t1; drop table t1;