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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, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (722) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00011

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "const",
      "possible_keys": ["PRIMARY", "product_id"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "ref": ["const", "const"],
      "rows": 1,
      "filtered": 100
    }
  }
}

Result

product_id	short_description	full_description	unit_name
722	<p>This range of prosthesis is entirely manufactured in France by experienced dental technicians, with more than ten years of expertise. By selecting this prosthesis, you are opting for the manufacture of a Full Zirconia Crown - Origin France - 3 days of Delay. A Full Zirconia crown is a monolithic restoration, it is therefore manufactured from a single material, zirconia, which is machined in the mass. The machined restoration is then tinted on the surface.</p>