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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 (56, 57, 55) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00088

JSON explain

{
  "query_block": {
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    "cost_info": {
      "query_cost": "4.22"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "product_id"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "product_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 3,
      "rows_produced_per_join": 3,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "3.62",
        "eval_cost": "0.60",
        "prefix_cost": "4.22",
        "data_read_per_join": "13K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "unit_name"
      ],
      "attached_condition": "((`twebezli_Commercemodalpopup`.`cscart_product_descriptions`.`product_id` in (56,57,55)) and (`twebezli_Commercemodalpopup`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id	short_description	full_description	unit_name
55		<p>The PRS-D800 2-channel amplifier contains audiophile grade components that were carefully selected and design perfected to achieve highest audio quality.</p>
56		<p>From dramatic distinction to dramatic design, Pioneer's new GM-Series amplifiers are thrillers in every sense, pushing the limits of flexibility and functionality.<br /><br />The 4-channel GM-6500F delivers a whopping 760 watts max - plenty of juice to power your speakers. It's also got built-in low-pass/high-pass crossovers, speaker level inputs for easy connection to an OEM headunit and oversized power terminals.</p>
57		<p>Class-D amplifiers overcome the inefficiencies of traditional Class-A or AB amplifiers. Pioneer’s Class-D amps transform very little power into heat so a higher percentage of the power supply (67%) is transformed into the load. This results in a very compact amp which needs less input power to produce very high output power. The Class-D amplifier’s PWM (Pulse Width Modulator) modulates the original audio input signal with a triangulated signal wave which has a much higher fixed frequency. The result is a digital signal which contains both the input signal and a band of frequency components around the modulation frequency. A LPF (Low Pass Filter) then filters out the high frequency pulses and the resulting amplified output signal is then sent to the subwoofer and/or speakers.</p>