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 (
    2478, 2527, 2490, 2471, 2576, 2620, 2502, 
    2473, 2565, 2580, 2550, 2599, 2503, 
    2602, 2540, 2685, 2623, 8398, 2499, 
    2581, 2631, 2519, 8399, 8397, 8395, 
    10140, 10222, 10228, 10233
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00121

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "20.54"
    },
    "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": 29,
      "rows_produced_per_join": 29,
      "filtered": "100.00",
      "index_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`product_id` in (2478,2527,2490,2471,2576,2620,2502,2473,2565,2580,2550,2599,2503,2602,2540,2685,2623,8398,2499,2581,2631,2519,8399,8397,8395,10140,10222,10228,10233)) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "17.64",
        "eval_cost": "2.90",
        "prefix_cost": "20.54",
        "data_read_per_join": "132K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}