SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '' 
    OR cscart_product_descriptions.short_description IS NULL, 
    cscart_product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    149469, 149461, 149615, 149689, 149472, 
    149687, 149482, 149608, 149610, 149457, 
    149573, 149467, 149455, 149688, 149638, 
    149673, 149640, 149667, 149585, 149670, 
    149665, 149481, 149617, 149605, 149664, 
    392444, 392445, 149587
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00148

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "39.26"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 28,
      "rows_produced_per_join": 28,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "33.66",
        "eval_cost": "5.60",
        "prefix_cost": "39.26",
        "data_read_per_join": "191K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`webmarco`.`cscart_product_descriptions`.`product_id` in (149469,149461,149615,149689,149472,149687,149482,149608,149610,149457,149573,149467,149455,149688,149638,149673,149640,149667,149585,149670,149665,149481,149617,149605,149664,392444,392445,149587)) and (`webmarco`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}