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LAG
Value function. 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 which 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 example (a int, b int);
insert into example values(1,2),(2,2),(3,3),(4,3);
select a,lag(a) over(order by (a)) from 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 example;
+------+-----------------------------+
| a | lag(a,2) over(order by (a)) |
+------+-----------------------------+
| 1 | NULL |
| 2 | NULL |
| 3 | 1 |
| 4 | 2 |
+------+-----------------------------+
