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 (
    1515, 1514, 1512, 423, 2708, 4555, 421, 
    1967, 422, 4558, 2723, 7735, 7734, 6193, 
    7737, 6195, 6194, 7736, 7750, 6196, 
    4415, 4417, 4414, 4412, 4416, 7588, 
    7589, 7590, 7591, 7592, 7240, 7237, 
    7236, 7238, 7239, 5875, 5877, 5874, 
    5879, 5880, 5873, 5876, 5878, 5881, 
    5872, 3999, 4004, 4005
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00094

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 (1515,1514,1512,423,2708,4555,421,1967,422,4558,2723,7735,7734,6193,7737,6195,6194,7736,7750,6196,4415,4417,4414,4412,4416,7588,7589,7590,7591,7592,7240,7237,7236,7238,7239,5875,5877,5874,5879,5880,5873,5876,5878,5881,5872,3999,4004,4005)) 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"
      ]
    }
  }
}