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 (
    4138, 4184, 5025, 4177, 4119, 4196, 4343, 
    4139, 4211, 4356, 4140, 4286, 4288, 
    4594, 4552, 4179, 4638, 4208, 4300, 
    4593, 4640, 4907, 4906, 4502, 4890, 
    4596, 4586
  ) 
  AND cscart_product_descriptions.lang_code = 'ar'

Query time 0.00081

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "19.12"
    },
    "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": 27,
      "rows_produced_per_join": 27,
      "filtered": "100.00",
      "index_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`product_id` in (4138,4184,5025,4177,4119,4196,4343,4139,4211,4356,4140,4286,4288,4594,4552,4179,4638,4208,4300,4593,4640,4907,4906,4502,4890,4596,4586)) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`lang_code` = 'ar'))",
      "cost_info": {
        "read_cost": "16.43",
        "eval_cost": "2.70",
        "prefix_cost": "19.13",
        "data_read_per_join": "123K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ]
    }
  }
}