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 (
    6303, 6304, 5801, 5802, 5800, 5799, 5803, 
    5804, 7197, 7195, 7196, 7190, 7189, 
    7194, 7191, 5032, 5033, 7674, 7675, 
    6967, 6966, 6645, 6644, 6647, 6648, 
    4352, 4354, 5391, 5392, 5388, 5390, 
    5389, 5396, 5395, 5394, 5034, 5035, 
    5030, 5031, 5168, 5169, 6982, 6132, 
    7150, 7149, 7148, 7151, 6768
  ) 
  AND cscart_product_descriptions.lang_code = 'de'

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 (6303,6304,5801,5802,5800,5799,5803,5804,7197,7195,7196,7190,7189,7194,7191,5032,5033,7674,7675,6967,6966,6645,6644,6647,6648,4352,4354,5391,5392,5388,5390,5389,5396,5395,5394,5034,5035,5030,5031,5168,5169,6982,6132,7150,7149,7148,7151,6768)) and (`dbggbern`.`cscart_product_descriptions`.`lang_code` = 'de'))",
      "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"
      ]
    }
  }
}