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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c78b1125511c13410e9c4175cb8eaaf4c284cc3678a41c0f80b388aa74e48c42' 
  AND token = 'kf71mcRw+3mpEeHdFo91ZWlfOZQsy5lg1nchheEHhZs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00041

JSON explain

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