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 (
    49164, 47903, 49230, 28159, 43817, 48846, 
    1894, 23152, 47631, 1533, 6372, 49873, 
    6358, 6357, 41341, 35279, 47597, 47084, 
    5787, 1767, 3866, 5503, 18608, 2139, 
    42255, 40350, 3867, 23158, 2957, 1057, 
    5790, 33723
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00525

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 (49164,47903,49230,28159,43817,48846,1894,23152,47631,1533,6372,49873,6358,6357,41341,35279,47597,47084,5787,1767,3866,5503,18608,2139,42255,40350,3867,23158,2957,1057,5790,33723) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}