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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    426897, 415377, 388453, 389558, 390161, 
    390193, 390198, 389507, 388957, 415496, 
    389263, 390209, 390316, 388958, 390273, 
    389359, 388544, 388479, 389452, 390257, 
    388513, 389873, 390129, 389532, 390192, 
    389827, 388454, 390243, 390164, 389428
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00126

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "42.06"
    },
    "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": 30,
      "rows_produced_per_join": 30,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "36.06",
        "eval_cost": "6.00",
        "prefix_cost": "42.06",
        "data_read_per_join": "204K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`webmarco`.`cscart_product_descriptions`.`product_id` in (426897,415377,388453,389558,390161,390193,390198,389507,388957,415496,389263,390209,390316,388958,390273,389359,388544,388479,389452,390257,388513,389873,390129,389532,390192,389827,388454,390243,390164,389428)) and (`webmarco`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}