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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    85935, 85940, 85941, 85933, 85939, 85959, 
    85957, 85931, 85932, 85930, 85954, 
    85953, 85950, 85951, 85948, 85909, 
    85910, 85911, 85906, 85907, 85908
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00038

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "9.47"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 21,
      "rows_produced_per_join": 21,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "7.37",
        "eval_cost": "2.10",
        "prefix_cost": "9.47",
        "data_read_per_join": "80K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (85935,85940,85941,85933,85939,85959,85957,85931,85932,85930,85954,85953,85950,85951,85948,85909,85910,85911,85906,85907,85908)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
85906 Nuie Mayford Floor Standing 555mm Unit & WC - Gloss White
85907 Nuie Mayford Floor Standing 555mm Unit & WC - Gloss White
85908 Nuie Mayford Floor Standing 420mm Unit & WC - Gloss White
85909 Nuie Mayford Floor Standing 480mm Unit & WC - Gloss White
85910 Nuie Mayford Floor Standing 450mm Unit & WC - Gloss White
85911 Nuie Mayford Wall Hung 450mm Unit & WC - Gloss White
85930 Nuie Core Wall Hung 400mm Unit Tap & WC - Satin White
85931 Nuie Core Wall Hung 400mm Unit Tap & WC - Satin Anthracite
85932 Nuie Core Wall Hung 400mm Unit Tap & WC - Satin Green
85933 Nuie Core Wall Hung 500mm Unit Tap & WC - Satin White
85935 Nuie Core Wall Hung 500mm Unit Tap & WC - Satin Green
85939 Nuie Core Floor Standing 400mm Unit Tap & WC - Satin White
85940 Nuie Core Floor Standing 400mm Unit Tap & WC - Satin Anthracite
85941 Nuie Core Floor Standing 400mm Unit Tap & WC - Satin Green
85948 Nuie Vault Wall Hung 400mm Unit WC & Tap - Gloss White
85950 Nuie Vault Wall Hung 400mm Unit WC & Tap - Anthracite Woodgrain
85951 Nuie Vault Wall Hung 400mm Unit WC & Tap - Charcoal Black
85953 Nuie Vault Wall Hung 400mm Unit WC & Tap - Gloss Grey
85954 Nuie Vault Floor Standing 400mm Unit WC & Tap - Gloss White
85957 Nuie Vault Floor Standing 400mm Unit WC & Tap - Charcoal Black
85959 Nuie Vault Floor Standing 400mm Unit WC & Tap - Gloss Grey