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 (
    2044, 2047, 49003, 49030, 49703, 41434, 
    41432, 48783, 49010, 49107, 321, 41433, 
    49028, 49016, 49009, 49008, 49204, 
    49205, 50285, 50347, 50213
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00246

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": 21,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (2044,2047,49003,49030,49703,41434,41432,48783,49010,49107,321,41433,49028,49016,49009,49008,49204,49205,50285,50347,50213) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}