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 (
    38750, 31914, 48179, 4172, 859, 4171, 
    4170, 2801, 28127, 2761, 862, 6187, 
    4016, 6086, 4180, 4175, 6084, 31919, 
    227, 35377, 230, 33185, 31917, 6087, 
    4274, 2054, 1549, 506, 2800, 31915, 
    507, 3837
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00296

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 (38750,31914,48179,4172,859,4171,4170,2801,28127,2761,862,6187,4016,6086,4180,4175,6084,31919,227,35377,230,33185,31917,6087,4274,2054,1549,506,2800,31915,507,3837) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}