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 (
    3751, 3758, 3759, 3762, 47563, 3748, 
    4042, 4596, 4656, 4646, 3766, 4623, 
    3761, 4039, 3763, 6513, 6260, 4598, 
    4640, 46714, 4632, 47280, 6403, 6259, 
    48062, 6258, 4603, 6257, 47197, 47855, 
    47367, 4635
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00306

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 (3751,3758,3759,3762,47563,3748,4042,4596,4656,4646,3766,4623,3761,4039,3763,6513,6260,4598,4640,46714,4632,47280,6403,6259,48062,6258,4603,6257,47197,47855,47367,4635) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}