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 (
    3568, 17265, 3567, 5990, 27359, 34555, 
    31638, 31633, 5300, 3517, 5991, 3516, 
    5297, 1579, 1980, 31634, 35782, 3518, 
    40445, 40442, 31639, 3570, 3569, 31636, 
    1979, 17259, 398, 1981, 40446, 31637, 
    5278, 47020
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.02206

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 (3568,17265,3567,5990,27359,34555,31638,31633,5300,3517,5991,3516,5297,1579,1980,31634,35782,3518,40445,40442,31639,3570,3569,31636,1979,17259,398,1981,40446,31637,5278,47020) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}