Rule Definition
It is useless to have several indexes on the same column(s) or to have an index on columns already covered by a composite index. This will not improve read performance and will decrease update/insert/delete performance because of index maintenance.

Remediation
Drop the index that are not necessary.

Violation Code Sample

-- SQL Sample
create table MyTable ( C1 int identity, C2 int)

create index MyTable_I1 on MyTable( C1)
create index MyTable_I2 on MyTable( C1)
create index MyTable_I3 on MyTable( C1, C2)

Fixed Code Sample

-- SQL Sample
create table MyTable ( C1 int identity, C2 int)

-- create index MyTable_I1 on MyTable( C1)
-- This index is useless as it is the same as MyTable_I2

-- create index MyTable_I2 on MyTable( C1)
-- This index is nearly useless as queries using C1 will be covered by the index MyTable_I3. It can then be dropped.


create index MyTable_I3 on MyTable( C1, C2)