How Can I Calculate the Difference Between Consecutive Rows in a SQL SELECT Statement?

Calculating Differences Between Sequential Rows in SQL Queries

Efficiently determining the difference between values in adjacent rows within a SQL SELECT statement is achievable using the LAG() window function. This streamlined approach avoids the complexities of subqueries or temporary tables.

Consider a table with Id and Value columns. To compute the difference between a row's Value and the preceding row's Value, employ this SQL syntax:

<code class="language-sql">SELECT Value - LAG(Value) OVER (ORDER BY Id) AS Difference
FROM your_table;</code>

The LAG(Value) function retrieves the Value from the row preceding the current row, ordered by the Id column. Subtracting this lagged value from the current Value yields the difference.

It's crucial to note the ORDER BY clause within the OVER() function. If your Id column is not a continuous sequence, using Id - 1 would be inaccurate. LAG() reliably handles gaps in the sequence by referencing the previous row based on the specified order.

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