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 (51, 10, 9) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00040

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.11"
    },
    "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": 3,
      "rows_produced_per_join": 3,
      "filtered": "100.00",
      "index_condition": "((`betaatif_store`.`cscart_product_descriptions`.`product_id` in (51,10,9)) and (`betaatif_store`.`cscart_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "1.81",
        "eval_cost": "0.30",
        "prefix_cost": "2.11",
        "data_read_per_join": "11K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ]
    }
  }
}

Result

product_id short_description full_description
9 <p><span><strong>BEDROOM CONTAINS OF : </strong><strong>BED + 2 COMEDINO + DRESSER WITH MIRROR + CHAIR + CHEST OF DRAWER + CUPBOARD 6 SASH</strong></span></p>
10 <p><span><strong>BEDROOM CONTAINS OF : </strong><strong>BED + 2 COMEDINO + DRESSER WITH MIRROR + CHAIR + CHEST OF DRAWER + CUPBOARD 6 SASH</strong></span></p>
51 <p><strong>SOFA SET CONTAIN OF:  2 THREE SEAT SOFA + 1 TWO SEAT SOFA</strong></p> <p><strong>THREE SEAT SOFA: LENGTH 100 * WIDTH 250 * HEIGHT 100 CM</strong></p> <p><strong>TWO SEAT SOFA : LENGTH 100 * WIDTH 180 * HEIGHT 100 CM</strong></p>