Structure de eex_symbols_reference:
  id | int(11) | NO | PRI
  symbol_native | varchar(255) | NO | UNI
  symbol_api_format | varchar(255) | NO | MUL
  symbol_stored_format | varchar(255) | NO | MUL
  symbol_type | enum('FUTURES','SPOT','POWER_SPOT') | NO | MUL
  market_category | enum('POWER','GAS','EUA','CO2') | NO | MUL
  country_code | varchar(10) | YES | MUL
  country_name | varchar(50) | YES | 
  product_type | enum('BASE','PEAK','DAY_AHEAD','WEEKEND','NEXT_DAY') | YES | MUL
  period_type | enum('YEAR','QUARTER','MONTH','SEASON','DAILY') | YES | 
  exchange_name | varchar(50) | YES | 
  description_fr | text | YES | 
  description_en | text | YES | 
  is_active | tinyint(1) | YES | 
  created_at | timestamp | NO | 
  updated_at | timestamp | NO | 

Premiers enregistrements:
  {"id":1,"symbol_native":"\/E.F7BYF{year}","symbol_api_format":"\"\/E.F7BYF{year}\"","symbol_stored_format":"\/E.F7BYF{year}","symbol_type":"FUTURES","market_category":"POWER","country_code":"F7","country_name":"France","product_type":"BASE","period_type":"YEAR","exchange_name":"EEX","description_fr":"Futures \u00e9lectricit\u00e9 France Base - Ann\u00e9e","description_en":"France Power Base Load Futures - Year","is_active":1,"created_at":"2026-01-27 09:42:10","updated_at":"2026-01-27 09:42:10"}
  {"id":2,"symbol_native":"\/E.F7BQF{year}","symbol_api_format":"\"\/E.F7BQF{year}\"","symbol_stored_format":"\/E.F7BQF{year}","symbol_type":"FUTURES","market_category":"POWER","country_code":"F7","country_name":"France","product_type":"BASE","period_type":"QUARTER","exchange_name":"EEX","description_fr":"Futures \u00e9lectricit\u00e9 France Base - Trimestre","description_en":"France Power Base Load Futures - Quarter","is_active":1,"created_at":"2026-01-27 09:42:10","updated_at":"2026-01-27 09:42:10"}
  {"id":3,"symbol_native":"\/E.F7BMF{year}","symbol_api_format":"\"\/E.F7BMF{year}\"","symbol_stored_format":"\/E.F7BMF{year}","symbol_type":"FUTURES","market_category":"POWER","country_code":"F7","country_name":"France","product_type":"BASE","period_type":"MONTH","exchange_name":"EEX","description_fr":"Futures \u00e9lectricit\u00e9 France Base - Mois","description_en":"France Power Base Load Futures - Month","is_active":1,"created_at":"2026-01-27 09:42:10","updated_at":"2026-01-27 09:42:10"}