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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8068d1938b7b9e02033962f3326073974e4bf1483bd766fefd1a6286a126c28' 
  AND token = 'MENaK1UDnckSHjrOFv8QDrtmDaG3YaLcbVOTUtndcUw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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