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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '251d5d4d1d34c6cc90faa1eb1f14fa3176bf6a254731c920851f8ee0e6ea51ee' 
  AND token = '/M6yzApTr6L8CdPgIl4FzbRV+Jlmf0KqVNtI5EKBKOc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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