code: public function findUniqueIndexes($table)
      {
          $result = [];
          foreach ($this->findTableConstraints($table, 'UNIQUE') as $row) {
              $result[$row['index_name']][] = $row['field_name'];
          }
  
          return $result;
      }
docs: Returns all unique indexes for the given table.
  
  Each array element is of the following structure:
  
  ```php
  [
  'IndexName1' => ['col1' [, ...]],
  'IndexName2' => ['col2' [, ...]],
  ]
  ```
  
  @param TableSchema $table the table metadata
  @return array all unique indexes for the given table.
  @since 2.0.4