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 (
    50698, 50699, 50695, 50671, 50684, 50676, 
    50673, 50348, 50264, 50524, 50527, 
    50305, 50345, 50517, 50612, 50214, 
    50302, 50341, 50417, 50605, 50650, 
    50630, 50244, 50347, 50349, 50621, 
    50626, 50326, 50276, 50278
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00507

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": 30,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (50698,50699,50695,50671,50684,50676,50673,50348,50264,50524,50527,50305,50345,50517,50612,50214,50302,50341,50417,50605,50650,50630,50244,50347,50349,50621,50626,50326,50276,50278) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}