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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76b387731970d9a54cd00b91a3f649c0ac8d61446faed00eb9504dc32d952aed' 
  AND token = '6D0u9xUeFGp8+9ou0aBKseg0jL3ifT38YbQajlGEKW8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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