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 (
    4603, 4606, 4623, 4629, 4625, 4605, 4577, 
    4578, 4630, 4631, 4556, 4607, 4633, 
    4634, 4576, 4575, 4627, 4608, 4622, 
    4619, 4632, 4626, 4628, 4620, 4580, 
    4621, 4609
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00132

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 (4603,4606,4623,4629,4625,4605,4577,4578,4630,4631,4556,4607,4633,4634,4576,4575,4627,4608,4622,4619,4632,4626,4628,4620,4580,4621,4609)) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "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"
      ]
    }
  }
}