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 (
    21487, 21488, 21489, 21490, 21491, 21492, 
    21493, 21494, 21495, 21496, 21497, 
    21498, 21499, 21500, 21501, 21502
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00051

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 (21487,21488,21489,21490,21491,21492,21493,21494,21495,21496,21497,21498,21499,21500,21501,21502) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id short_description full_description unit_name
21487 Duct-rear heating rear, right<p>Part number 97375T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21488 Duct - rear heating, right<p>Part number 97370T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21489 Grille Assembly - Air Extractor<p>Part number 97510T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21490 Clip-Air Conditioner Cooler Line<p>Part number 977944D920</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21491 Clip-pipe mounting<p>Part number 97794T6500</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21492 Rubber-Mounting<p>Part number 978572B050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21493 Sensor-Ambient<p>Part number 969850X000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21494 Bolt-Washer Assembly<p>Part number 1142506306B</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21495 BOLT<p>Part number 1140308187K</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21496 O-ring<p>Part number 9769034350</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21497 compressor assembly<p>Part number 97701T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21498 Seal - Air Conditioning Compressor Shaft<p>Part number 9770733300</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21499 Hose-Discharge<p>Part number 97762T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21500 hose-suction<p>Part number 97763T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21501 Bracket-Suction Hose Mounting<p>Part number 97794T6300</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21502 Tube Assemblies - Suction & Liquid<p>Part number 97775T6050</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>