SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19629, 19630, 19631, 19632, 19633, 19634, 
    19635, 19636, 19637, 19638, 19639, 
    19640, 19641, 19642, 19643, 19644
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00377

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id", "idx_product_lang"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (19629,19630,19631,19632,19633,19634,19635,19636,19637,19638,19639,19640,19641,19642,19643,19644) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}