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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '81ca50be1903d83a3214d668eff4f2f24762bffcdca25a1601e56180dee2131b' 
  AND token = '1fp6PlkxtMYRO30Fznw7df3EDFe8VEiqkhqpk04NXKU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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