Author: Ian

An Introduction to the MEDIAN() Function in SQL

Posted on by Ian

Some relational database management systems (RDBMSs) have a MEDIAN() function that calculates the median value within a range of values.

It returns the middle value or an interpolated value that would be the middle value once the values are sorted.

The SQL MEDIAN() function typically operates on numeric expressions, but depending on the RDBMS, may also operate on other data types, such as datetime expressions.

Depending on the RDBMS, the MEDIAN() function can be used as a window function, as an aggregate function, or as both.

Continue reading →

How to Fix Error “function lead(numeric, numeric) does not exist” in PostgreSQL

Posted on by Ian

If you’re getting an error in PostgreSQL that reads something like “function lead(numeric, numeric) does not exist“, it may be because your second argument is of the wrong data type.

The second argument to the lead() function is optional, but if it’s provided, it must be an integer.

To fix this issue, make sure the second argument is an integer. Alternatively, you can omit the second argument altogether if you’re happy to use the default value of 1.

Continue reading →

Introduction to the PERCENTILE_DISC() Function in SQL

Posted on by Ian

Some SQL databases have a PERCENTILE_DISC() function that calculates a percentile based on a discrete distribution of a range of column values.

We specify the percentile to use when we call the function.

Depending on the DBMS, PERCENTILE_DISC() can be used as a window function, as an aggregate function, or as both.

The PERCENTILE_DISC() function always returns a value from the underlying data. This is in contrast to the PERCENTILE_CONT() function, which can interpolate between adjacent values to return a value that’s not in the underlying data.

Continue reading →

Overview of the PERCENTILE_CONT() Function in SQL

Posted on by Ian

Some relational database management systems (RDBMSs) have a PERCENTILE_CONT() function that calculates a percentile based on a continuous distribution across a range of column values.

We specify the percentile to use when we call the function.

Depending on the RDBMS, PERCENTILE_CONT() can be used as a window function or an aggregate function, or as both.

Continue reading →

How to Fix the Error: “The function ‘LEAD’ must have an OVER clause with ORDER BY” in SQL Server

Posted on by Ian

If you’re getting an error message that reads “The function ‘LEAD’ must have an OVER clause with ORDER BY” in SQL Server, it’s probably because you’ve omitted the ORDER BY clause from the OVER clause when using the LEAD() function.

The LEAD() function requires an OVER clause that contains an ORDER BY clause. This error happens when we include the OVER clause but not the ORDER BY clause.

To fix this error, add an ORDER BY clause to the OVER clause.

Continue reading →

Understanding the LAST_VALUE() Function in SQL

Posted on by Ian

In SQL databases, LAST_VALUE() is a window function that returns the last value in an ordered set of values. It allows us to get a value from the last row of a query result set or partition.

You may need to explicitly set the window frame if you want LAST_VALUE() to return the actual last value from the partition or result set. That’s because in many/most DBMSs, the default window frame ends with the current row.

Continue reading →