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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '3951d76d979b489b4f2bb3feb2e9b0186889c51104e2b88be2e3c868c179b0c0' 
  AND token = '9i3RI/31d2VGe55Abfwzk+ybTlxV6F42lynCj0qFVRE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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