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 (
    4724, 40141, 36574, 3821, 4719, 3818, 
    40144, 48822, 36573, 36503, 4731, 3820, 
    3819, 1064, 46188, 46272, 46271, 46270, 
    4733, 43265, 36575, 46169, 46190, 47185, 
    46168, 46263, 46171, 46187, 46173, 
    46170, 48817, 46172
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00867

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 (4724,40141,36574,3821,4719,3818,40144,48822,36573,36503,4731,3820,3819,1064,46188,46272,46271,46270,4733,43265,36575,46169,46190,47185,46168,46263,46171,46187,46173,46170,48817,46172) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}