# Access rows before and after current row

Use LAG and LEAD window functions to access values from surrounding rows

Access values from rows before and after the current row to find patterns, detect changes, or provide context around events.

## Problem

You want to see values from surrounding rows alongside the current row - for example, the 5 previous and 5 next bid prices for each row.

## Solution

Use `LAG()` to access rows before the current row and `LEAD()` to access rows after:

```questdb-sql demo title="Access surrounding row values with LAG and LEAD"
SELECT timestamp, bid_price,
  LAG(bid_price, 1) OVER () AS prev_1,
  LAG(bid_price, 2) OVER () AS prev_2,
  LAG(bid_price, 3) OVER () AS prev_3,
  LAG(bid_price, 4) OVER () AS prev_4,
  LAG(bid_price, 5) OVER () AS prev_5,
  LEAD(bid_price, 1) OVER () AS next_1,
  LEAD(bid_price, 2) OVER () AS next_2,
  LEAD(bid_price, 3) OVER () AS next_3,
  LEAD(bid_price, 4) OVER () AS next_4,
  LEAD(bid_price, 5) OVER () AS next_5
FROM core_price
WHERE timestamp IN '$now - 1m..$now' AND symbol = 'EURUSD';
```

## How it works

- **`LAG(column, N)`** - Gets the value from N rows **before** the current row (earlier in time)
- **`LEAD(column, N)`** - Gets the value from N rows **after** the current row (later in time)

Both functions return `NULL` for rows where the offset goes beyond the dataset boundaries (e.g., `LAG(5)` returns `NULL` for the first 5 rows).

:::info Related Documentation
- [LAG window function](/docs/query/functions/window-functions/reference/#lag)
- [LEAD window function](/docs/query/functions/window-functions/reference/#lead)
- [Window functions overview](/docs/query/functions/window-functions/syntax/)
:::