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 (
    50216, 50194, 40927, 6372, 6358, 6357, 
    31633, 1975, 2305, 49192, 2303, 6354, 
    31965, 26895, 26894, 38797, 26872, 
    47567, 26871, 26876, 26870, 26874, 
    26878, 26885, 26875, 26879, 26884, 
    1972, 44424, 5141, 297, 51
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00445

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 (50216,50194,40927,6372,6358,6357,31633,1975,2305,49192,2303,6354,31965,26895,26894,38797,26872,47567,26871,26876,26870,26874,26878,26885,26875,26879,26884,1972,44424,5141,297,51) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}