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 (
    21983, 21984, 21985, 21986, 21987, 21988, 
    21989, 21990, 21991, 21992, 21993, 
    21994, 21995, 21996, 21997, 21998
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00081

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 (21983,21984,21985,21986,21987,21988,21989,21990,21991,21992,21993,21994,21995,21996,21997,21998) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}

Result

product_id short_description full_description unit_name
21983 gear-rear line<p>Part number 457704J750</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21984 gear-rear line<p>Part number 457714J700</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21985 Gear Assembly - Rear Anulus<p>Part number 457964J700</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21986 Diff Assembly-Front<p>Part number 474004J501</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21987 Shaft Assembly - Propeller<p>Part number 49100T6700</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21988 Boot Kit - Wheel Side<p>Part number 495A4T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21989 Joint & Shaft Kit-Wheel Side, Left<p>Part number 495L1T6800</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21990 Joint kit-differential side, left<p>Part number 495L3T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21991 Boot kit - differential side, left<p>Part number 495L5T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21992 Damper kit, left<p>Part number 495L6T6800</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21993 Joint & Shaft Kit - Wheel Side, Right<p>Part number 495R1T6800</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21994 Joint kit-differential side, right<p>Part number 495R3T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21995 Boot kit - differential side, right<p>Part number 495R5T6000</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21996 Damper kit, right<p>Part number 495R6T6800</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21997 Shaft assembly - drive rear, left<p>Part number 49600T6400</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>
21998 Shaft assembly - drive rear, right<p>Part number 49601T6900</p><p>If you are not sure about compatibility, please contact us in advance to confirm the part number.</p>