-8018: Index name must be unique 

Explanation:

  1. This error message can occur when a <DROP INDEX statement> is executed. Indexes with identical names were created for separate tables. Therefore the name of the index to be deleted is not unique.
  2. There is only a named single-column index for this column. The attempt was made to delete the index for this column without specifying its name.

User Action:

  1. Specify the name of the table to which the index to be deleted refers in the <DROP INDEX statement>.
  2. Delete the index specifying its name.