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 (
    91409, 91411, 91413, 91415, 91417, 84304, 
    84305, 84632, 84633, 83303, 83305, 
    90553, 90554, 91100, 91101, 91104, 
    91105, 91107, 91108, 91109, 91186, 
    91187, 91190, 91191, 91193, 91194, 
    91195, 91241, 91242, 91245
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00107

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.52"
    },
    "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": 30,
      "rows_produced_per_join": 30,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "10.52",
        "eval_cost": "3.00",
        "prefix_cost": "13.52",
        "data_read_per_join": "114K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (91409,91411,91413,91415,91417,84304,84305,84632,84633,83303,83305,90553,90554,91100,91101,91104,91105,91107,91108,91109,91186,91187,91190,91191,91193,91194,91195,91241,91242,91245)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
83303 nuie Athena Floor Standing 4 Drawer Vanity With Twin Polymarble Basin 1200mm - Gloss White
83305 nuie Athena Floor Standing 4 Drawer Vanity With Twin Ceramic Basin 1200mm - Gloss White
84304 Hudson Reed Fusion Floor Standing 4 Door Vanity Basin Left Hand Combination 1200mm - Gloss White
84305 Hudson Reed Fusion Floor Standing 4 Door Vanity Basin Right Hand Combination 1200mm - Gloss White
84632 Hudson Reed Fusion Floor Standing 2 Door Vanity Basin & WC Left Hand Combination 1200mm - Gloss Grey
84633 Hudson Reed Fusion Floor Standing 2 Door Vanity Basin & WC Right Hand Combination 1200mm - Gloss Grey
90553 Nuie Arno 1200mm Floor Standing 4 Drawer Vanity & Double Basin 1 - Gloss White
90554 Nuie Arno 1200mm Floor Standing 4 Drawer Vanity & Double Basin 2 - Gloss White
91100 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Anthracite/Black
91101 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Anthracite/Black
91104 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Anthracite/Grey
91105 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Anthracite/Grey
91107 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Anthracite/White
91108 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Anthracite/White
91109 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Square Basin, 800mm - Satin Anthracite
91186 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Grey/Black
91187 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Grey/Black
91190 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Grey/Grey
91191 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Grey/Grey
91193 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Grey/White
91194 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Grey/White
91195 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Square Basin, 800mm - Satin Grey/White
91241 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Green/Black
91242 nuie Classique Floor Standing 2 Door Unit & 3 Tap Hole Marble Top with Oval Basin, 800mm - Satin Green/Black
91245 nuie Classique Floor Standing 2 Door Unit & 1 Tap Hole Marble Top with Oval Basin, 800mm - Satin Green/Grey
91409 Hudson Reed Old London Floor Standing 2 Door Vanity Unit & 3 Tap Hole Fireclay Basin, 600mm - Timeless Sand
91411 Hudson Reed Old London Floor Standing 2 Door Vanity Unit & 0 Tap Hole Fireclay Basin, 600mm - Timeless Sand
91413 Hudson Reed Old London Floor Standing 2 Door Vanity Unit & 1 Tap Hole Fireclay Basin, 600mm - Hunter Green
91415 Hudson Reed Old London Floor Standing 2 Door Vanity Unit & 3 Tap Hole Fireclay Basin, 600mm - Hunter Green
91417 Hudson Reed Old London Floor Standing 2 Door Vanity Unit & 0 Tap Hole Fireclay Basin, 600mm - Hunter Green