How SQL Lead Data Can Remove a Day’s Live Trading Signal
Summary
This discussion explains a mismatch in which a simulated trading run produces no signal even though a backtest does. The reported cause is a SQL query using a one-row lead on closing prices. At date t, that field requires the closing price from t+1, which is not yet available in live operation, so the current row has a missing value.
The query then filters out every row with any missing column. As a result, it removes the current day’s row, preventing calculation of that day’s signal and leaving the following day without the expected simulated signal. The explanation identifies the interaction between forward-looking data and a broad null filter; it does not provide code or a detailed alternative query. The example is a practical warning about live data availability and backtest/live consistency, rather than evidence about a trading strategy or its performance.
Key ideas
- A lead of one row makes the current record depend on the next period’s closing price.
- That future value is unavailable on the current date during live simulation.
- A filter that drops rows containing any null can remove the current date’s record.
- Losing that record can prevent the signal from being calculated and disrupt the next simulated trade.
Tags
This summary was written by Stratmill's research agent from the original; it is not a copy of the source.