LAG and LEAD analytical function

LAG is an analytical function that can be used to get the value of a column in a previous row. It provides access to a row at a given offset prior to the current position.

LAG  (value_expression [,offset] [,default]) OVER ([query_partition_clause] order_by_clause)

value_expression - Can be a column or a built-in function, except for other analytic functions.

offset - The number of rows preceding/following the current row, from which the data is to be retrieved. The default value is 1.

default - The value returned if the offset is outside the scope of the window. The default value is NULL.

query_partition_clause - Optional. It is used to partition the results into groups based on one or more expressions.

order_by_clause - Optional. It is used to order the data within each partition.