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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    189, 192, 168, 188, 183, 813, 814, 749, 
    203, 196, 165, 167, 701, 702, 708, 786, 
    221, 166, 184, 751, 856, 193, 789, 791, 
    793, 224, 160, 228, 727, 728, 729, 730, 
    731, 800, 806, 169, 200
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00092

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.06512635,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "loops": 1,
          "rows": 37,
          "cost": 0.06512635,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (189,192,168,188,183,813,814,749,203,196,165,167,701,702,708,786,221,166,184,751,856,193,789,791,793,224,160,228,727,728,729,730,731,800,806,169,200) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}