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 (
    8987, 8990, 8992, 8993, 8994, 8996, 8997, 
    8999, 9003, 9004, 9005, 9006, 9009, 
    9011, 9020, 9021
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00042

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 (8987,8990,8992,8993,8994,8996,8997,8999,9003,9004,9005,9006,9009,9011,9020,9021) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
8987 Hose-PCSV<p>Part number 289123NTA0</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8990 Stay-Surge Tank<p>Part number 292163N100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8992 insulator<p>Part number 292132F900</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8993 Rubber-Mounting<p>Part number 292442E000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8994 ETC-Actuator<p>Part number 351003NTQ0</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8996 Fuel Rail-MPI<p>Part number 353043NTC0</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8997 Clip-Fuel Injector<p>Part number 3530925000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
8999 Harness-injector<p>Part number 353023NTC0</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9003 E-module<p>Part number 4630547700</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9004 bolt<p>Part number 1140306301</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9005 transfer assembly<p>Part number 4730047100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9006 Diff Assembly-Front<p>Part number 4740047611</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9009 bolt<p>Part number 49319T6100</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9011 bolt<p>Part number 49319T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9020 bolt<p>Part number 1129410256P</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
9021 Bolt-flange<p>Part number 1140306126B</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>