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 (
    40808, 37295, 5772, 351, 4887, 2565, 
    37298, 1052, 1850, 37486, 2155, 6527, 
    26858, 26848, 5759, 47592, 2626, 406, 
    6526, 26862, 3621, 41130, 31622, 4889, 
    37280, 31902, 21746, 2250, 35466, 26863, 
    43796, 1051
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00712

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "11",
          "used_key_parts": ["product_id", "lang_code"],
          "rows": 32,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (40808,37295,5772,351,4887,2565,37298,1052,1850,37486,2155,6527,26858,26848,5759,47592,2626,406,6526,26862,3621,41130,31622,4889,37280,31902,21746,2250,35466,26863,43796,1051) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}