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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'fb22f198e0366fbe1aad6e6b4b84d310a7198001cb6f6f97eacb852097557b51' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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