SELECT 
  product_descriptions.product_id, 
  product_descriptions.short_description, 
  IF(
    product_descriptions.short_description = '' 
    OR product_descriptions.short_description IS NULL, 
    product_descriptions.full_description, 
    ''
  ) AS full_description 
FROM 
  product_descriptions 
WHERE 
  product_descriptions.product_id IN (20899, 57337, 262510) 
  AND product_descriptions.lang_code = 'en'

Query time 0.00056

JSON explain

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      "key": "PRIMARY",
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      "filtered": "100.00",
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        "lang_code",
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      ],
      "attached_condition": "((`goimagine`.`product_descriptions`.`product_id` in (20899,57337,262510)) and (`goimagine`.`product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id short_description full_description
20899 <p>Natural coconut and sea shell beaded ankle bracelet for men or women. Personalized sizes and finish.</p>
57337 <p>Adorable, lazy sloth charm hangs on a leather cord necklace. Individually hand made in your choice of colors, mint, tan or black and lengths from 13 to 20 inches.</p>
262510 <p>Verdigris patina copper sea turtle pendant necklace for both Men and Women.</p> <p>Beautifully finished on both top and bottom with different designs, this turtle charm is made of&nbsp;lead-free base metal covered in copper and given an antiqued verdigris patina.</p> <p>Necklace is made in your choice of length and leather colors for a fully customized look.&nbsp;</p> <p>Turtle charm - 1 1/8" x 1 1/8" (28mmx28mm)</p> <p>Closes with a copper lobster claw closure.</p> <p>This turtle necklace has a fun surfer vibe for your waterman. Makes a great gift for any occasion for your favorite beach loving man or woman.&nbsp;</p>