Returns the row before the current one in a partition based on the
ORDER BY clause without the need for a self-join. If there are no rows, this function returns
LAG(expression, [offset]) OVER ([PARTITION BY partition_expression][ORDER BY order_expression]) → same as input type
- expression (optional): An expression that is returned.
- offset: An optional parameter. The number of rows before the current row from which to obtain a value. Supports only a value of 1.
- partition_expression (optional): An optional expression that groups rows into partitions.
- order_expression: An optional expression that specifies the order of the rows within each partition.
PARTITION BY "Category"
ORDER BY "DayOfWeek")
-- Category, Descript, DayOfWeek, EXPR$3
-- ARSON, ARSON, Friday, null
-- ARSON, ARSON, Friday, Friday