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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 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    85914, 85915, 85919, 85946, 85947, 85912, 
    85945, 85926, 85923, 85928, 85921, 
    85943, 85944, 85942, 85937, 85938, 
    85936, 85934, 85935, 85940, 85941, 
    85933, 85939, 85959, 85957, 85931, 
    85932, 85930, 85954, 85953
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00076

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "13.52"
    },
    "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": 30,
      "rows_produced_per_join": 30,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "10.52",
        "eval_cost": "3.00",
        "prefix_cost": "13.52",
        "data_read_per_join": "114K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description"
      ],
      "attached_condition": "((`nuie_scalesta_net`.`cscart_product_descriptions`.`product_id` in (85914,85915,85919,85946,85947,85912,85945,85926,85923,85928,85921,85943,85944,85942,85937,85938,85936,85934,85935,85940,85941,85933,85939,85959,85957,85931,85932,85930,85954,85953)) and (`nuie_scalesta_net`.`cscart_product_descriptions`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id	short_description	full_description
85912	Nuie Merit Wall Hung 500mm Unit WC & Tap - Gloss White
85914	Nuie Merit Wall Hung 500mm Unit WC & Tap - Anthracite Woodgrain
85915	Nuie Merit Wall Hung 500mm Unit WC & Tap - Charcoal Black
85919	Nuie Merit Wall Hung 500mm Unit WC & Tap - Electric Blue
85921	Nuie Merit Slimline Wall Hung 500mm Unit WC & Tap - Gloss White
85923	Nuie Merit Slimline Wall Hung 500mm Unit WC & Tap - Anthracite Woodgrain
85926	Nuie Merit Slimline Wall Hung 500mm Unit WC & Tap - Gloss Grey
85928	Nuie Merit Slimline Wall Hung 500mm Unit WC & Tap - Electric Blue
85930	Nuie Core Wall Hung 400mm Unit Tap & WC - Satin White
85931	Nuie Core Wall Hung 400mm Unit Tap & WC - Satin Anthracite
85932	Nuie Core Wall Hung 400mm Unit Tap & WC - Satin Green
85933	Nuie Core Wall Hung 500mm Unit Tap & WC - Satin White
85934	Nuie Core Wall Hung 500mm Unit Tap & WC - Satin Anthracite
85935	Nuie Core Wall Hung 500mm Unit Tap & WC - Satin Green
85936	Nuie Core Wall Hung 600mm Unit Tap & WC - Satin White
85937	Nuie Core Wall Hung 600mm Unit Tap & WC - Satin Anthracite
85938	Nuie Core Wall Hung 600mm Unit Tap & WC - Satin Green
85939	Nuie Core Floor Standing 400mm Unit Tap & WC - Satin White
85940	Nuie Core Floor Standing 400mm Unit Tap & WC - Satin Anthracite
85941	Nuie Core Floor Standing 400mm Unit Tap & WC - Satin Green
85942	Nuie Core Floor Standing 500mm Unit Tap & WC - Satin White
85943	Nuie Core Floor Standing 500mm Unit Tap & WC - Satin Anthracite
85944	Nuie Core Floor Standing 500mm Unit Tap & WC - Satin Green
85945	Nuie Core Floor Standing 600mm Unit Tap & WC - Satin White
85946	Nuie Core Floor Standing 600mm Unit Tap & WC - Satin Anthracite
85947	Nuie Core Floor Standing 600mm Unit Tap & WC - Satin Green
85953	Nuie Vault Wall Hung 400mm Unit WC & Tap - Gloss Grey
85954	Nuie Vault Floor Standing 400mm Unit WC & Tap - Gloss White
85957	Nuie Vault Floor Standing 400mm Unit WC & Tap - Charcoal Black
85959	Nuie Vault Floor Standing 400mm Unit WC & Tap - Gloss Grey