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 (
    31638, 3870, 114, 47923, 1582, 2143, 
    33312, 31633, 31632, 3287, 3286, 3872, 
    113, 5300, 3517, 5991, 2144, 3516, 33744, 
    5297, 1980, 1103, 65, 5543, 31634, 5784, 
    41281, 6652, 3518, 41282, 40445, 40442
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.02209

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 (31638,3870,114,47923,1582,2143,33312,31633,31632,3287,3286,3872,113,5300,3517,5991,2144,3516,33744,5297,1980,1103,65,5543,31634,5784,41281,6652,3518,41282,40445,40442) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}