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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '399a4d8a12fc792c2c8b532e0e886f1ed3099af675dded2d4d52518f74de1804' 
  AND token = '8N1BLdkIwIi1EA+PQ45poMx+VIh37vgOYel/ImKR7lw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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