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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 (3750, 3749, 3936, 3937) 
  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 (3750,3749,3936,3937)",
      "attached_condition": "cscart_product_descriptions.lang_code = 'en'"
    }
  }
}

Result

product_id	full_description	search_words
3749	<p> Protect your EVX-S24 radio with a Vertex Standard leather carrying case with belt loops to hold the radio firmly to the belt.</p>	EVX-S24 Case
3750	<p> This leather carrying case protects EVX-S24 radio and allows the user to secure the radio to his belt. The swivel belt loop allows the radio to easily move with the user from sitting to standing to bending.</p>	EVX-S24 Case
3936	<p> Protect your EVX-S24 radio with a leather carrying case with belt loops to hold the radio firmly to the belt.</p>	EVX-S24 Case
3937	<p> This leather carrying case protects EVX-S24 radio and allows the user to secure the radio to his belt. The swivel belt loop allows the radio to easily move with the user from sitting to standing to bending.</p>	EVX-S24 Case