SELECT 
  com.company, 
  cpi.company_id, 
  GROUP_CONCAT(
    cpi.impact_id 
    ORDER BY 
      cpi.position
  ) as impact_ids 
FROM 
  cscart_companies AS com 
  LEFT JOIN cscart_company_positive_impacts AS cpi ON cpi.company_id = com.company_id 
WHERE 
  cpi.company_id = 99

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}

Result

company company_id impact_ids