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SELECT 
  p.*, 
  d.*, 
  images.promotion_image_id 
FROM 
  cscart_promotions as p 
  LEFT JOIN cscart_promotion_descriptions as d ON p.promotion_id = d.promotion_id 
  AND d.lang_code = 'ru' 
  LEFT JOIN cscart_promotion_images AS images ON images.promotion_id = p.promotion_id 
  AND images.lang_code = 'ru' 
WHERE 
  p.promotion_id = 14

Query time 0.00037

JSON explain

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