lag
open fun <T> ExpressionWithColumnType<T>.lag(offset: ExpressionWithColumnType<Int> = intLiteral(1), defaultValue: ExpressionWithColumnType<T>? = null): Lag<T>
Returns value evaluated at the row that is offset rows before the current row within the partition; if there is no such row, instead returns defaultValue. Both offset and defaultValue are evaluated with respect to the current row.