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 (
    40706, 39407, 40230, 31724, 39680, 39404, 
    39401, 39406, 39405, 39144, 39403, 
    40778, 31725, 31727, 30418, 30420, 
    30413, 30414, 30415, 30416, 30417, 
    30421, 30423, 31732, 39408, 39409, 
    39410
  ) 
  AND cscart_product_descriptions.lang_code = 'fr'

Query time 0.00054

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "64.81"
    },
    "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": 27,
      "rows_produced_per_join": 27,
      "filtered": "100.00",
      "index_condition": "((`ea201_diorama`.`cscart_product_descriptions`.`product_id` in (40706,39407,40230,31724,39680,39404,39401,39406,39405,39144,39403,40778,31725,31727,30418,30420,30413,30414,30415,30416,30417,30421,30423,31732,39408,39409,39410)) and (`ea201_diorama`.`cscart_product_descriptions`.`lang_code` = 'fr'))",
      "cost_info": {
        "read_cost": "59.41",
        "eval_cost": "5.40",
        "prefix_cost": "64.81",
        "data_read_per_join": "103K"
      },
      "used_columns": [
        "product_id",
        "lang_code",
        "short_description",
        "full_description",
        "meta_keywords",
        "meta_description",
        "search_words",
        "promo_text"
      ]
    }
  }
}