When we create a window function in SQL, we have the option of defining it directly in the OVER clause or in a named window. When we define it in a named window, we can refer to that window name in our OVER clause, which saves us from having to define it directly in the OVER clause.
Author: Ian
Understanding the RANK() Function in SQL
In SQL databases, the RANK() function is a window function that returns the rank of the current row within its partition, with gaps.
By “with gaps” I mean that if there are any ties for a given rank, there will be a gap between that rank value and the next rank value.
If you don’t want such gaps, use the DENSE_RANK() function instead, as it returns the rank without gaps.
Understanding the CUME_DIST() Function in SQL
Many relational database management systems (RDBMSs) provide us with a range of window functions.
The CUME_DIST() function is a window function that’s commonly implemented in RDBMSs for the purpose of calculating the cumulative distribution across a data set. In other words, it calculates the relative position of a specified value in a group of values.
Fix Error “The function ‘DENSE_RANK’ must have an OVER clause with ORDER BY” in SQL Server
If you’re getting an error that reads “The function ‘DENSE_RANK’ must have an OVER clause with ORDER BY” in SQL Server, it’s probably because you’re calling the DENSE_RANK() function without an ORDER BY clause.
Window functions such as DENSE_RANK() require an OVER clause, and that clause must have an ORDER BY clause. If you’re getting the above error, it’s likely that you’re providing an OVER clause, but you’re omitting the ORDER BY clause.
To fix this error, add an ORDER BY clause to the OVER clause.
How to Skip Rows that Fail a CHECK Constraint in MySQL
Normally if we try to insert data that violates a CHECK constraint in MySQL, we get an error, and the whole INSERT operation fails (including any conforming rows).
But it’s possible to change this, so that any conforming rows are inserted, and only the non-conforming rows are skipped.
We can do this by using the IGNORE clause.
Using the LAST_VALUE() Function to Get the Value from the Last Row in PostgreSQL
In PostgreSQL the last_value() function returns the value from the last row of the current window frame.
2 Possible Reasons You’re Getting “function nth_value(numeric) does not exist” in PostgreSQL
There are at least a couple of reasons you might get an error that reads “function nth_value(numeric) does not exist” in PostgreSQL.
It could be that you’re calling the nth_value() function without the correct number of arguments. It could also be that you’re passing the wrong argument type.
To fix this issue, be sure to pass the correct number of arguments, with the correct type.
Continue readingUsing the FIRST_VALUE() Function to Get the Value from the First Row in PostgreSQL
In PostgreSQL the first_value() function returns the value from the first row in the current window frame.
We can use this function to get the value from the first row in a result set, or from the first row in the current partition, or some other window frame that’s been specified.
Continue readingUnderstanding the sys.ps_is_consumer_enabled() Function in MySQL
In MySQL, we can use the sys.ps_is_consumer_enabled() function to check whether a given Performance Schema consumer is enabled.
The function returns YES or NO, depending on whether or not the specified Performance Schema consumer is enabled. It returns NULL if the argument is NULL.
Overview of the MODE() Function in PostgreSQL
PostgreSQL has an ordered-set aggregate function called mode() that allows us to get the mode from a given column.
The mode is the most frequently occurring value.
Null values are ignored, so if null occurs the most, the mode() function will return the second most common value.