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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21ee3e8b8beec04caffffb539697688beda6587052450467ee6df2689254be2e' 
  AND token = 'ZOcyVXE1RNHcWL1kFy6BZRJc1bcW5Lib2ffOOS2h+EA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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