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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 (4124, 4072, 5077, 5121, 4949, 4955) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00028

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": 6,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (4124,4072,5077,5121,4949,4955)",
      "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id	full_description	search_words
4072		VL50 Headset, Headsets/Lapel Mics/Surveillance Kits
4124	<p>Designed for moderate-noise environments, this accessory lets users enjoy communication that's clear, private and hands-free. This lightweight, single-muff headset is comfortable for extended wear and has a swivel boom microphone. No adapters required. </p>	VL50 Headset, Headsets/Lapel Mics/Surveillance Kits
4949
4955	<p>Motorola BDN6774 - Earpiece with Microphone</p><p> (worn over ear with streamlined boom microphone)</p>
5077
5121	<p>Bone conduction enables you to receive audio without covering your ears, allowing you to either wear hearing protection in extreme-noise environments or keep your ears open to external sounds. This lightweight Temple Transducer with in-line push-to-talk and microphone provides clear audio while providing comfort for extended wear.</p>