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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c4cc14ef7f16e470e5b684347baa74deb121cddba19ee8d66235b7cedb35bf58' 
  AND token = '4PYJz8N5eeN41poExAw87SZTweER7k6tgiPiGjmUcIo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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