SELECT 
  q_product_descriptions.product_id, 
  q_product_descriptions.short_description, 
  IF(
    q_product_descriptions.short_description = '', 
    q_product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  q_product_descriptions 
WHERE 
  q_product_descriptions.product_id IN (
    40744, 40745, 40758, 40759, 40761, 40768, 
    40769, 40770, 40776, 40788, 40789, 
    40790, 40791, 40792, 40793, 40794, 
    40795, 40796, 40809, 40821, 40827, 
    40828, 40829, 40830, 40831, 40832, 
    40833, 40834, 40835, 40836, 40837, 
    40839
  ) 
  AND q_product_descriptions.lang_code = 'en'

Query time 0.00074

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "76.81"
    },
    "table": {
      "table_name": "q_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": 32,
      "rows_produced_per_join": 32,
      "filtered": "100.00",
      "index_condition": "((`portal`.`q_product_descriptions`.`product_id` in (40744,40745,40758,40759,40761,40768,40769,40770,40776,40788,40789,40790,40791,40792,40793,40794,40795,40796,40809,40821,40827,40828,40829,40830,40831,40832,40833,40834,40835,40836,40837,40839)) and (`portal`.`q_product_descriptions`.`lang_code` = 'en'))",
      "cost_info": {
        "read_cost": "70.41",
        "eval_cost": "6.40",
        "prefix_cost": "76.81",
        "data_read_per_join": "122K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ]
    }
  }
}

Result

product_id short_description full_description
40744
40745
40758
40759
40761
40768
40769
40770
40776 <p style="padding:0px;margin-top:0em;margin-bottom:1em;margin-left:1em;font-family:'Amazon Ember', Arial, sans-serif;font-size:small;background-color:rgb(255,255,255);">Intex - Inflatable Canopy Island<br /><br />This beautiful island will give you hours of relaxation on the water. Its has space for two people and is provided with a removable visor and two drink holders. It also has a rope and two air chambers for added security.<br /><br />Features:</p><ul><li>Dimensions: 199 x 150 cm</li><li>Includes 1 repair patch</li></ul>
40788
40789
40790
40791 <ul><li>Brand: INTEX</li> <li>Model Number : 58439NP</li> <li>PACKAGE TYPE : PRINTED BOX</li> <li>CASE PACK : 6</li> <li>Product Size : 58"X13"</li> <li>NO.OF ASSORTMENT : 1</li> <li>Age Grading : 2+</li> </ul>
40792 <ul class="a-unordered-list a-vertical a-spacing-none"><li><span class="a-list-item">Ideal for ages 3 and up</span></li> <li><span class="a-list-item">3 separate and Equal Rings</span></li> <li><span class="a-list-item">Repair Patch Included</span></li> </ul>
40793
40794
40795 <ul class="a-unordered-list a-vertical a-spacing-none"><li><span class="a-list-item">Brand : Intex</span></li> <li><span class="a-list-item">Product weight : 10.6 kg</span></li> <li><span class="a-list-item">Targeted Group : Unisex</span></li> <li><span class="a-list-item">Age : 6 Years & above</span></li> <li><span class="a-list-item">Outdoor Play Activities : Swim pool</span></li> <li><span class="a-list-item">Recommended Age : 3 - 6 Years</span></li> </ul>
40796
40809
40821 <ul class="a-unordered-list a-vertical a-spacing-none"><li><span class="a-list-item">A sweet and refreshing addition to your pool this summer</span></li> <li><span class="a-list-item">Fun pineapple design</span></li> <li><span class="a-list-item">85'' x 49'', 12ga vinyl</span></li> <li><span class="a-list-item">Repair patch included</span></li> </ul>
40827
40828
40829
40830
40831
40832
40833
40834
40835
40836
40837
40839