Database Management Systems
In MySQL, we can use the LEAD() function to get the value of a subsequent row. For example we can get a value from the next row, or the one after that, and so on.
This enables us to do things like compute the difference between a value in the current row and a value in a following row. We can do this even if both values are in the same column.
Continue readingIf you’re getting an error that reads “window function nth_value requires an OVER clause” in PostgreSQL, it’s because you’re calling the nth_value() function without an OVER clause.
PostgreSQL requires that you include an OVER clause any time you call a built in nonaggregate window function such as nth_value().
To fix this issue, add an OVER clause to your window function.
MySQL 8.0.17 introduced a couple of functions that allow us to validate JSON documents against their schemas. These are listed below, with examples.
Continue readingIf you’re getting an error that reads “The function ‘CUME_DIST’ must have an OVER clause” when using SQL Server, it’s because you’re calling the CUME_DIST() function without an OVER clause.
The CUME_DIST() function requires an OVER clause (and that clause must have an ORDER BY clause).
To fix this issue, be sure to include an OVER clause when calling the CUME_DIST() function.
In SQL Server, the CUME_DIST() function calculates and returns the cumulative distribution of a value within a group of values. This is the relative position of a specified value in a group of values.
Below is a list of functions that can be used as window functions in MySQL.
Some are nonaggregate functions that can only be used as window functions, while others are aggregate functions that can be used as window functions if required.
Continue readingIn PostgreSQL the lead() function returns the value from a subsequent row to the current row, specified by the given offset.
The offset specifies how many rows after the current row to get the value from. For example, an offset of 1 gets the value from the next row.
In PostgreSQL the lag() function returns the value from a previous row, specified by the given offset.
The offset specifies how many rows prior to the current row to get the value from. For example, an offset of 1 gets the value from the previous row.
In PostgreSQL the nth_value() function is a window function that returns the value from the given row of the current window frame. We provide the column and row number as an argument when we call the function.
In PostgreSQL, we can use the cume_dist() function to return the cumulative distribution of a value within a group of values.
It calculates this as follows: (the number of partition rows preceding or peers with current row) / (total partition rows).
The return value ranges from 1/N to 1.