The SQLite LEAD function is a window function that allows you to access the value of a subsequent row within the same result set, based on a specified column order. It can be used to calculate various types of analytical and reporting queries that require access to values from other rows in a table.
The syntax for using the LEAD function in SQLite is as follows:
LEAD(column_expression [, offset [, default_value]]) OVER (PARTITION BY partition_expression ORDER BY order_expression [ASC|DESC])
Here, column_expression represents the name of the column whose values you want to retrieve from the next row. offset is an optional integer value that specifies the number of rows to skip before returning the value. The default_value parameter is also optional, and allows you to specify a default value to return if no subsequent row is found.
The PARTITION BY clause is used to group the result set into partitions, based on one or more columns. The ORDER BY clause is used to specify the column order that determines the sequence in which rows are processed. You can specify the order as either ascending (ASC) or descending (DESC).
Here’s an example of how you can use the LEAD function in SQLite:
SELECT name, sales, LEAD(sales) OVER (ORDER BY sales DESC) as next_sales FROM sales_table;
In this example, the query returns the name and sales values from the sales_table, along with the value of the next row’s sales value in the result set. The LEAD function is used to retrieve the value of the subsequent row’s sales column, based on the descending order of the sales column.