Many RDBMSs include both a rank() and a dense_rank() function in their list of window function offerings. At first glance, these functions might appear to do the same thing. However, there’s one important difference between these functions, and you will definitely need to be aware of this difference when choosing which function to use.
Author: Ian
Understanding the FETCH Clause in Oracle
Oracle Database has a FETCH clause that allows us to limit the number of rows returned by a SELECT statement.
We can use this clause to specify the exact number of rows or the percentage of rows that a query should return. We can also specify an offset for which to start.
Continue readingUsing the ROW_NUMBER() Function to get Row Numbers in SQL
The SQL ROW_NUMBER() function is a window function that assigns and returns a row number of each row in a query partition or result set. Numbering starts at 1 and increments sequentially.
This enables us to add a “row number” column to our queries.
Continue readingAn Introduction to the MEDIAN() Function in SQL
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.
How to Fix Error “function lead(numeric, numeric) does not exist” in PostgreSQL
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.
Understanding the MODE() Function in SQL
Some SQL relational database management systems (RDBMSs) have a MODE() function that returns the most frequently occurring value from all row values in a column.
The mode is the value that appears most frequently in a data set.
Continue readingIntroduction to the PERCENTILE_DISC() Function in SQL
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.
Overview of the PERCENTILE_CONT() Function in SQL
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.
An Introduction to the PERCENT_RANK() Function in SQL
Many relational database management systems (RDBMSs) provide a window function called PERCENT_RANK() that returns the relative rank of a row within a group of rows.
The relative rank is expressed as a value between 0 and 1.
Continue readingHow to Fix the Error: “The function ‘LEAD’ must have an OVER clause with ORDER BY” in SQL Server
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.