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Returns a value evaluated at the row that is at a specified physical offset before the current row within the ordered frame. This function is similar to lagInFrame, but always uses the ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING frame. Syntax 
lag(x[, offset[, default]])
  OVER ([[PARTITION BY grouping_column] [ORDER BY sorting_column]] | [window_name])
FROM table_name
WINDOW window_name as ([[PARTITION BY grouping_column] [ORDER BY sorting_column])
For more detail on window function syntax see: Window Functions - Syntax. Parameters
  • x — Column name.
  • offset — Offset to apply. (U)Int*. (Optional - 1 by default).
  • default — Value to return if calculated row exceeds the boundaries of the window frame. (Optional - default value of column type when omitted).
Returned value
  • Value evaluated at the row that is at a specified physical offset before the current row within the ordered frame.
Example This example looks at historical data for a specific stock and uses the lag function to calculate a day-to-day delta and percentage change in the closing price of the stock.
Query
CREATE TABLE stock_prices
(
    `date`   Date,
    `open`   Float32, -- opening price
    `high`   Float32, -- daily high
    `low`    Float32, -- daily low
    `close`  Float32, -- closing price
    `volume` UInt32   -- trade volume
)
Engine = Memory;

INSERT INTO stock_prices FORMAT Values
    ('2024-06-03', 113.62, 115.00, 112.00, 115.00, 438392000),
    ('2024-06-04', 115.72, 116.60, 114.04, 116.44, 403324000),
    ('2024-06-05', 118.37, 122.45, 117.47, 122.44, 528402000),
    ('2024-06-06', 124.05, 125.59, 118.32, 121.00, 664696000),
    ('2024-06-07', 119.77, 121.69, 118.02, 120.89, 412386000);
Query
SELECT
    date,
    close,
    lag(close, 1, close) OVER (ORDER BY date ASC) AS previous_day_close,
    COALESCE(ROUND(close - previous_day_close, 2)) AS delta,
    COALESCE(ROUND((delta / previous_day_close) * 100, 2)) AS percent_change
FROM stock_prices
ORDER BY date DESC
Response
   ┌───────date─┬──close─┬─previous_day_close─┬─delta─┬─percent_change─┐
1. │ 2024-06-07 │ 120.89 │                121 │ -0.11 │          -0.09 │
2. │ 2024-06-06 │    121 │             122.44 │ -1.44 │          -1.18 │
3. │ 2024-06-05 │ 122.44 │             116.44 │     6 │           5.15 │
4. │ 2024-06-04 │ 116.44 │                115 │  1.44 │           1.25 │
5. │ 2024-06-03 │    115 │                115 │     0 │              0 │
   └────────────┴────────┴────────────────────┴───────┴────────────────┘