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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.meta_keywords, 
  cscart_product_descriptions.meta_description, 
  cscart_product_descriptions.search_words, 
  cscart_product_descriptions.promo_text, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (30, 29) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00047

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "product_id",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 2,
          "filtered": 100,
          "index_condition": "cscart_product_descriptions.product_id in (30,29)",
          "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}

Result

product_id	short_description	full_description	meta_keywords	meta_description	search_words	promo_text	unit_name
29		<p>The TomTom GO LIVE Top Gear edition satnav! Featuring the voice of Jeremy Clarkson, plus a heap of Top Gear bonus goodies, this special edition satnav is the ultimate traffic- vanquishing weapon for the discerning driverist. With speed camera warnings, information via Local Search with Google™, weather reports and more, it’ll spirit you onto gloriously empty roads when all about you are stuck in jams. With the calming presence of Jeremy Clarkson himself by your side, what could possibly go wrong?</p>				<p class="product-promo-text"><span class="product-promo-header">FREE US shipping over $100!</span><span class="product-promo-body">Orders within next 2 days will be shipped on Monday</span></p>
30		<p>The TomTom GO series is the ultimate in driving intelligence. The new, super-slim TomTom GO series holds the latest navigation technology, in a fresh, sleek design and includes a magnetic, click & lock mount for maximum mounting security. Travel confidently with superior routing and the most accurate, dependable maps in the GPS industry.</p>				<p class="product-promo-text"><span class="product-promo-header">FREE US shipping over $100!</span><span class="product-promo-body">Orders within next 2 days will be shipped on Monday</span></p>