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.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 (
    40826, 40509, 40510, 38833, 40495, 35693, 
    40431, 38832, 38830, 38795, 38569, 
    40038, 37005, 40042, 40043, 40141, 
    40140, 38788, 38831, 39090, 38875, 
    32009, 39089, 40062, 39441, 39354, 
    39353, 36377, 39385, 39076
  ) 
  AND cscart_product_descriptions.lang_code = 'fr'

Query time 0.00054

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "72.01"
    },
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "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",
      "index_condition": "((`ea201_diorama`.`cscart_product_descriptions`.`product_id` in (40826,40509,40510,38833,40495,35693,40431,38832,38830,38795,38569,40038,37005,40042,40043,40141,40140,38788,38831,39090,38875,32009,39089,40062,39441,39354,39353,36377,39385,39076)) and (`ea201_diorama`.`cscart_product_descriptions`.`lang_code` = 'fr'))",
      "cost_info": {
        "read_cost": "66.01",
        "eval_cost": "6.00",
        "prefix_cost": "72.01",
        "data_read_per_join": "114K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "meta_keywords",
        "meta_description",
        "search_words",
        "promo_text"
      ]
    }
  }
}