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 (
    40532, 49309, 36293, 44568, 44574, 4374, 
    45364, 36521, 44573, 4385, 45365, 40529, 
    44571, 40534, 36470, 47257, 25162, 
    47258, 47393, 44570, 24788, 40531, 
    2048, 49758
  ) 
  AND cscart_product_descriptions.lang_code = 'vi'

Query time 0.00910

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": 24,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (40532,49309,36293,44568,44574,4374,45364,36521,44573,4385,45365,40529,44571,40534,36470,47257,25162,47258,47393,44570,24788,40531,2048,49758) and cscart_product_descriptions.lang_code = 'vi'"
        }
      }
    ]
  }
}