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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21ba28e937b1d70b61a8727e4a38e592e3c7c485d2128ed26be39bd5b1152351' 
  AND token = '5bWqQUy0gw2bB4pHF+w7zpiEziqIntHVdJViI4e7EFQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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