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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51a0881f4df9c588c9e0fa13b021069ca4cc23a5e5a66e02c8b20ed0c8aaeba8' 
  AND token = 'Zt9OwMVHq/MMIkvUOMDyJI/aBbccphwWnTJ7zlt7wec=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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