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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '300b9e27007a8b2bee4629cdaa4b76634398acd78953f7bc8df5847adc9be8be' 
  AND token = 'jgdSJZuUY085D1oQH2UNU9OIjKYlfHIxt/rvM4p/RL8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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