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 (
    4974, 4995, 4992, 5008, 4991, 5969, 5024, 
    5017, 5002, 4988, 5007, 5019, 5010, 
    5018, 5005, 5011, 5014, 5021, 5022, 
    5006, 4961, 5009, 5013, 4989, 5004, 
    5020, 5016, 5023, 9699
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00127

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 (4974,4995,4992,5008,4991,5969,5024,5017,5002,4988,5007,5019,5010,5018,5005,5011,5014,5021,5022,5006,4961,5009,5013,4989,5004,5020,5016,5023,9699)) 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"
      ]
    }
  }
}