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SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.short_description, 
  IF(
    cscart_product_descriptions.short_description = '', 
    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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (5990, 5995, 5996, 5994) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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": 4,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (5990,5995,5996,5994)",
      "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id	short_description	full_description
5990	<p>Product Features:</p><p>Video Manager System (VMS) Software License Required: $2,250.00</p><p>Remote Alarm Activation</p><p>Up to 12 hours of continuous recording</p><p>64 GB of recording storage capacity</p><p>Full HD (1920 X 1080) recording</p><p>Bluetooth and Wi-Fi connectivity</p><p>Flexible mounting options</p><p>Secure file encryption</p><p>Encrypted GPS receiver</p><p>Pre and Post Recording Capability</p>
5994		<p>Custom VB400 front-button Sticker (Print). Qty. 250</p>
5995		<p>Custom VB400 front-button Sticker (Print). Qty. 1000</p>
5996		<p>Custom VB400 front-button Sticker (Print). Qty. 5000</p>