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 (
    31639, 31640, 31642, 31641, 31643, 31652, 
    31651, 31649, 31650, 31647, 31645, 
    31646, 31644
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00302

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": 13,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (31639,31640,31642,31641,31643,31652,31651,31649,31650,31647,31645,31646,31644) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}