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SingleStoreDB v7.6

LAG

Returns an expression evaluated at some offset before the current row.

If there is no such row returns NULL instead.

Syntax

LAG ( expression [, offset]) OVER (
    [PARTITION BY (col | expr), ...] 
    [ORDER BY (col | expr), ...]
)

Arguments

  • expression: any expression. This may be a column name, the result of another function, or a math operation

  • offset: A constant integer that specifies the number of rows before the current row to evaluate the expression. Defaults to 1 if not specified

Return Type

The result of expression

Examples

CREATE TABLE lag_example (a int, b int);

INSERT INTO lag_example VALUES(1,2),(2,2),(3,3),(4,3);

SELECT a, LAG(a) OVER(ORDER BY (a)) FROM lag_example;

****
+------+---------------------------+
| a    | LAG(a) OVER(ORDER BY (a)) |
+------+---------------------------+
|    1 |                      NULL |
|    2 |                         1 |
|    3 |                         2 |
|    4 |                         3 |
+------+---------------------------+
SELECT a, LAG(a,2) OVER(ORDER BY (a)) FROM lag_example;

****
+------+-----------------------------+
| a    | LAG(a,2) OVER(ORDER BY (a)) |
+------+-----------------------------+
|    1 |                        NULL |
|    2 |                        NULL |
|    3 |                           1 |
|    4 |                           2 |
+------+-----------------------------+
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