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 (
    2340, 2352, 2339, 2338, 2341, 10213, 
    2337, 10237, 8439, 10249, 10058, 10239, 
    10103, 10160, 10242, 10246, 10044, 
    10099, 10106, 10166, 10256, 10046, 
    10107, 10108, 10162, 10165
  ) 
  AND cscart_product_descriptions.lang_code = 'ar'

Query time 0.00105

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.42"
    },
    "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": 26,
      "rows_produced_per_join": 26,
      "filtered": "100.00",
      "index_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`product_id` in (2340,2352,2339,2338,2341,10213,2337,10237,8439,10249,10058,10239,10103,10160,10242,10246,10044,10099,10106,10166,10256,10046,10107,10108,10162,10165)) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`lang_code` = 'ar'))",
      "cost_info": {
        "read_cost": "15.82",
        "eval_cost": "2.60",
        "prefix_cost": "18.42",
        "data_read_per_join": "118K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}