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 (
    6736, 613, 617, 3119, 3121, 5039, 5038, 
    5037, 5036, 5406, 6679, 5407, 5408, 
    4041, 6974, 7819, 7181, 7179, 1195, 
    1197, 1196, 6135, 6134, 6133, 2234, 
    2233, 6697, 4801, 4802, 5955, 5973, 
    5451, 5453, 5452, 5450, 5454, 5456, 
    5455, 5448, 5467, 5469, 5462, 5472, 
    5463, 5464, 5468, 5466, 5470
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00069

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "33.61"
    },
    "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": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "index_condition": "((`dbggbern`.`cscart_product_descriptions`.`product_id` in (6736,613,617,3119,3121,5039,5038,5037,5036,5406,6679,5407,5408,4041,6974,7819,7181,7179,1195,1197,1196,6135,6134,6133,2234,2233,6697,4801,4802,5955,5973,5451,5453,5452,5450,5454,5456,5455,5448,5467,5469,5462,5472,5463,5464,5468,5466,5470)) and (`dbggbern`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "28.81",
        "eval_cost": "4.80",
        "prefix_cost": "33.61",
        "data_read_per_join": "183K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "product",
        "short_description",
        "full_description"
      ]
    }
  }
}