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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76e51daf1ba40d405ea557189ea5940047de2db084863019dcb5401ffce2f39c' 
  AND token = 'fRU7s4frSHbMwapF78sg50/EclOB4ZskQusfnM7dhkM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}