SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.product, 
  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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    5783, 5602, 5228, 5969, 5524, 3424, 5558, 
    5559, 5555, 5557, 186, 7032, 7031, 7028, 
    7029, 7030, 7033, 6757, 6759, 6758, 
    3742, 7470, 4038, 3039, 3040, 3420, 
    3461, 3548, 3547, 5077, 5983, 129, 5937, 
    5970, 1824, 7034
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00072

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "25.21"
    },
    "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": 36,
      "rows_produced_per_join": 36,
      "filtered": "100.00",
      "index_condition": "((`dbggbern`.`cscart_product_descriptions`.`product_id` in (5783,5602,5228,5969,5524,3424,5558,5559,5555,5557,186,7032,7031,7028,7029,7030,7033,6757,6759,6758,3742,7470,4038,3039,3040,3420,3461,3548,3547,5077,5983,129,5937,5970,1824,7034)) and (`dbggbern`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "21.61",
        "eval_cost": "3.60",
        "prefix_cost": "25.21",
        "data_read_per_join": "137K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "product",
        "short_description",
        "full_description"
      ]
    }
  }
}