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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    51, 48, 54, 250, 69, 254, 184, 133, 132, 
    125, 120, 161, 163, 164, 147, 146, 145, 
    117, 113, 148, 149, 68, 6, 249, 248, 140, 
    141, 144, 143, 142, 63, 66
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.01536

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": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "rows": 32,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (51,48,54,250,69,254,184,133,132,125,120,161,163,164,147,146,145,117,113,148,149,68,6,249,248,140,141,144,143,142,63,66) and cscart_product_descriptions.lang_code = 'ru'"
        }
      }
    ]
  }
}