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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b6539fcd7e28f7bc7e9764fcd1d2dd1f5a28b844d52c77e2876f2f7519562dca' 
  AND token = 'v/xxiacbejRkXb8Xebqjpnvl4P/lcXLozkEjRi9ZKsc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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